Sales tax exemption certificates protect your business during an audit. If you sell to a customer tax-free and can’t produce a valid certificate when the state asks, you owe the tax plus penalties and interest. The state doesn’t care that your customer claimed they were exempt. Without documentation, you’re on the hook.

Request the certificate before you make the first tax-exempt sale, not after. Some businesses wait until year-end or until they realize they need it for record-keeping. By then, the customer may be unresponsive or the certificate may have expired before some of the transactions occurred. Make it part of your customer onboarding process for wholesale or tax-exempt accounts.

In Massachusetts, the form depends on who’s buying and why. Organizations with tax-exempt status like nonprofits and government agencies provide Form ST-2. Businesses buying goods for resale provide Form ST-5, also called a resale certificate. Other states have their own versions. If you’re selling to customers across state lines, you’ll need to collect the appropriate form for each state where you’re making tax-exempt sales.

Verify the certificate before you accept it. Check that the exemption type matches the purchase. A resale certificate only covers goods the buyer will resell, not office supplies for their own use. Make sure the certificate isn’t expired. In Massachusetts, ST-2 certificates include a registration number you can verify with the Department of Revenue.

Store certificates where you can actually find them. Paper files work for small volumes, but if you have dozens or hundreds of exempt customers, you need a better system. Some accounting software and sales tax platforms let you attach certificates to customer records. Whatever method you use, organize by customer name and state so you can pull the documentation quickly if the state comes asking.

The multi-state piece gets complicated. Each state has different exemption rules, different forms, and different validity periods. What qualifies as exempt in one state may not be exempt in another. Keeping track of which certificates you have, which are expiring, and which customers still need to submit theirs requires ongoing attention.

Don’t rely on verbal claims or emails saying “we’re tax exempt.” Without proper documentation on file, you’re exposed. An Andover, MA bookkeeper familiar with sales tax requirements can help you set up a process that captures certificates consistently and keeps your records audit-ready.