Washington State Auto Repair Rules for Mobile Mechanics: Estimates Over $100, the 10% Rule, and Sales Tax on Labor

Updated 2026-10-17. Sources are listed at the end.

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This is general information, not legal or tax advice. Rules vary by state and change often. Confirm with the official source linked in each section, or with a licensed attorney, CPA or insurance agent, before you act.

Washington doesn’t license mechanics or register repair shops through a separate program. Instead, the Automotive Repair Act (RCW 46.71) sets the rules for every “automotive repair facility,” meaning anyone who “for compensation engages in the business of automotive repair or diagnosis, or both” (RCW 46.71.011). That includes a one-person mobile operation. When the Department of Revenue issues your business registration, it’s required to notify you of the Act (RCW 46.71.090).

Not covered: commercial fleet work on two or more vehicles, and ongoing service contracts for vehicles used mainly for business (RCW 46.71.011(2)(a)). Fleet accounts work under your contract instead. See fleet maintenance accounts.

Estimates: over $100 must be in writing

Unless the customer waives it, an estimate over $100 must be in writing and include (RCW 46.71.015):

the date, plus your business name, address and phone
the customer’s name, address and phone (if available)
year, make, model, plate or last 8 of the VIN, and the odometer reading
the problem reported or the repairs requested
the three-option choice below

Before providing parts or labor, you must give a written estimate or offer the customer the statutory alternatives, using this wording, with initials or a signature (RCW 46.71.025):

A written estimate before repairs, and a call if the price will exceed it by more than 10%
Proceed, but call if the price will exceed $____
No written estimate

The 110% cap and how to record authorization

You may not charge more than 110% of the written estimate (excluding sales tax) unless the customer authorizes more, orally or in writing, before you do the extra work. For oral authorization, note on the estimate: the date and time, the added parts and labor, their estimated cost, who got the authorization, and the name and phone of the person who gave it (RCW 46.71.025(2)).

The penalties for skipping this:

You can’t recover more than 110% of the authorized amount in court unless you prove the charge was “reasonable, necessary, and justified” (RCW 46.71.035).
You lose your possessory lien for the unauthorized parts and labor if you don’t follow the estimate, parts-return or sign rules (RCW 46.71.041). That matters if you ever hold a car for payment. See customer won’t pay?
A violation counts as an unfair or deceptive act under Washington’s Consumer Protection Act (RCW 46.71.070).

Invoices

Every job gets an invoice, whether or not an estimate was required. It must include the estimate information plus the work performed, each part by name and part number (if available), whether parts are rebuilt or used, the price per part, total parts, total labor, and the total. Flat-rate menu items and advertised specials don’t need parts and labor split out (RCW 46.71.015(2)). Keep copies of estimates and invoices for at least one year. Electronic copies are fine if you can print them (RCW 46.71.060).

Replaced parts, warranties, and unlawful practices

If the customer asks when authorizing the repair, return the replaced parts. Parts under warranty or core return can be shown instead (RCW 46.71.021).
Give a copy of your written warranty on request (RCW 46.71.051). See writing a parts and labor warranty.
Unlawful practices include materially understating an estimate, charging for unnecessary repairs, and refusing to give the customer a free copy of anything they signed (RCW 46.71.045).

The sign

Facilities must post a sign stating customers’ rights, with the first line at least 1.5 inches tall (RCW 46.71.031). The Act assumes “business premises.” A mobile tech has no lobby, so a practical approach is to print the same wording on your estimate form. That doesn’t replace the posting rule. If you have a shop or office customers visit, post it there.

Sales tax: Washington taxes the whole repair, labor included

The Department of Revenue says repairs for consumers are retail sales, taxable under Retailing B&O “on the total charge made for the repair,” and retail sales tax must be collected on the total charge (WA DOR, Repairs). Parts you resell can be bought tax-free with a reseller permit. Tools, diagnostic equipment and consumable supplies you use up yourself are taxable to you. In the job quote & profit calculator, tick all three tax boxes for a Washington consumer job. Sales tax on auto repair compares other states.

Washington checklist

Register your business with the Department of Revenue (business license plus tax registration), and get a reseller permit for parts.
Use an estimate form with the RCW 46.71.025 three-option block. Whatever form or app you use, make sure the block uses the statute’s wording exactly.
Log every oral authorization: date, time, amount, who, and their phone.
Invoice part numbers and rebuilt/used status, and keep copies for one year or more. The IRS needs longer: see how long to keep records.
Collect sales tax on the full repair charge.

Sources

Revised Code of Washington, Chapter 46.71 (Automotive Repair): https://app.leg.wa.gov/RCW/default.aspx?cite=46.71&full=true
Washington Department of Revenue, Repairs (auto industry guide): https://dor.wa.gov/education/industry-guides/auto-dealers/repairs