What happens in a CDTFA sales tax audit of an out-of-state seller?

The sample, the error rate, and the two arguments that move it

The audit itself follows the sequence of Cal. Code Regs., tit. 18, section 1698.5: an engagement letter, an opening conference, an audit plan, information and document requests with stated response periods, findings presented for rebuttal, and an exit conference at which the auditor provides a complete copy of the audit working papers, with generally 30 days to respond. The substance, though, lives in the schedules: the auditor's summary of examined transactions, the exception items, and the computation projecting them. The representative's first job is reconciliation, comparing the auditor's exception list against the seller's own records, and the two recurring levers both come from that comparison.

The first is documentation credit. A resale certificate taken timely, at or before the sale or within the seller's normal billing and payment cycle (Cal. Code Regs., tit. 18, section 1668(a)), that sits uncredited in the exception schedules is pure assessment inflation; the fix is a certificate-by-certificate submission tied to the exception lines, pressed until the revised workpapers reflect it, since the difference between a certificate acknowledged and a certificate credited is the difference between a letter and a number. Where certificates were never collected, the cure is narrower than sellers expect: a certificate obtained during the audit is not retroactive and does not by itself relieve the seller (section 1668(e)). What late paper can do is serve as evidence, and relief then depends on showing that the property was in fact resold or is held for resale, or that the purchaser reported or paid the tax itself, usually through the XYZ letter procedure the regulation authorizes (section 1668(f)), with the Department weighing, and sometimes verifying, the responses rather than accepting them as certificates. The companion article on resale documentation covers that machinery and its limits.

The second lever is the treatment of large one-time sales, and how it works depends on the sampling method. In a block sample of test periods, the Department's Audit Manual allows a nonrecurring item to be excluded from the percentage of error, with all sales of a similar nature examined across the whole audit period and assessed separately; the test is the character of the transaction, such as an item much larger than normal that occurs only at rare intervals, one arising from an unusual circumstance, or a product the seller does not ordinarily handle, and the fact that a customer bought only once is not by itself a reason (CDTFA Audit Manual section 0405.20(e)). In a statistical sample, the Manual's preferred method, an error found in a selected sample item is scheduled and projected even when its circumstances were unusual, so known nonrecurring items must be disclosed before the sample is selected, when they can be removed from the population and scheduled on an actual basis (CDTFA Audit Manual section 1303.25, revised March 2023). On lumpy wholesale accounts the difference between a nonrecurring sale projected across years and one assessed as an actual item can dominate the assessment, which is why the issue is decided at the sampling-plan stage, before selection, rather than in the exception schedules afterward. Neither lever moves unless someone does the reconciliation.

Running the audit from out of state, and closing it

An out-of-state seller's audit has administrative friction a domestic audit lacks, and the friction costs money when ignored. Representation starts with the power of attorney, and a foreign entity often lacks the identifiers the form assumes, a federal employer identification number, sometimes even the Certificate of Registration-Use Tax number that an out-of-state retailer holds in place of a seller's permit (Cal. Code Regs., tit. 18, section 1684(e)(1)), particularly where the dispute is about registration itself; the sound course is a substitute identifier agreed with the auditor before the form is filed, because the auditor cannot discuss the audit until the authorization is in place, and weeks lost to a bounced POA are weeks of interest. An audit inherited mid-stream from a predecessor advisor calls for the same stabilization: immediate contact with the auditor, authorization re-established, and the current schedules in hand, because an audit gone quiet ripens toward the auditor's numbers. From there the audit advances by written revisions, each negotiated change reflected in an updated workpaper version, and the discipline of confirming every agreed adjustment in the next revision is what prevents the close-out surprise. Agreement costs nothing in appeal rights: agreeing to the audit findings during the audit does not preclude appealing the issues later (Cal. Code Regs., tit. 18, section 1698.5(c)(10)).

The endgame then runs on four levers. Prepayment: paying the expected liability before the formal billing stops interest from continuing to accrue on the amount paid, and the state's processes accommodate payment while the paperwork finishes. Interest mechanics: California computes interest on sales and use tax deficiencies by the month, and a fraction of a month costs the same as the whole month, with no daily proration, a method the statute fixes and the auditor cannot adjust (Rev. and Tax. Code section 6482). A payment that lands even one day into a further month of the computation carries that entire month's interest, and the statute does not say how the months are counted, so the sound practice is confirming the Department's month count before the funds move, because a month of interest paid for a day of delay is not an error anyone can fix afterward. One narrow relief provision exists: interest attributable to an unreasonable error or delay by a Department employee may be relieved, on a statement under penalty of perjury and only where no significant aspect of the error or delay is attributable to the taxpayer (Rev. and Tax. Code section 6593.5), a provision with obvious application to an audit that went dormant on the Department's side. Penalties: the structure splits by conduct, and the relief route splits with it. A seller that never filed faces the failure-to-file penalty of 10 percent of the tax (Rev. and Tax. Code section 6511), and that penalty the Department may relieve where the failure was due to reasonable cause and circumstances beyond the seller's control (Rev. and Tax. Code section 6592(a)(1)), so for the never-registered remote seller a written reasonable-cause showing is the right instrument. The negligence penalty is different arithmetic and a different route: Rev. and Tax. Code section 6484 adds 10 percent of the entire determination, but only where some part of the deficiency is due to negligence or intentional disregard of the law or authorized regulations, and section 6592 does not list section 6484, so a reasonable-cause request aimed at a negligence penalty is aimed at the wrong provision. The showing there is the absence of negligence, and the Department's own regulation supplies the strongest material for it: the negligence penalty generally should not be added to deficiency determinations associated with the first audit of a taxpayer, absent evidence that the errors cannot be attributed to the taxpayer's good faith and reasonable belief that its practices were in substantial compliance (Cal. Code Regs., tit. 18, section 1703(c)(3)(A)). A documentation-driven assessment built from certificates that existed but were not gathered, or from a characterization the seller held in good faith, therefore frequently carries no negligence penalty at all, and the first move at close is confirming what has been proposed rather than assuming. The petition: after the audit closes, the Department issues a notice of determination, and a petition for redetermination must be filed within 30 days after service or the determination becomes final (Rev. and Tax. Code section 6561). Those 30 days are the entire appeal window at that stage, and nothing agreed during the audit forecloses using them.

Practice notes

The sequence for any remote-seller CDTFA audit runs in a fixed order: authorization first, confirmed working before anything else, because the auditor cannot discuss the audit with an unauthorized representative; the exception schedules reconciled against the seller's records before any substantive response; certificates worked until they are credited in a revised workpaper, not merely received; nonrecurring items identified before a statistical sample is drawn, and in a block sample each such item documented as out of the ordinary in the terms the Audit Manual recognizes; and the close staged deliberately, agreed workpaper, prepayment timed against a confirmed interest computation, the 30-day petition deadline calendared the day the notice of determination arrives, any failure-to-file penalty answered on reasonable cause and any proposed negligence penalty answered in writing on the absence of negligence, with payment made through the online channels that document themselves. Prospectively, the audit converts into controls the same way its cousins do: certificate collection at onboarding rather than under audit, an exemption file organized by customer, and a registration posture that reflects how the seller touches California, the subject of the companion nexus article, because the second audit of a seller that fixed nothing is the same audit with more years in it. The registration question is about to widen: beginning January 1, 2027, specified digital products become taxable, and out-of-state sellers engaged in business in this state must register and collect use tax on them (SB 122, Stats. 2026, ch. 23; CDTFA Special Notice L1036, September 2026). G&G State Tax Group provides sales and use tax audit defense for remote and foreign sellers, from authorization and schedule reconciliation through the negotiated close, alongside its state and local tax practice.