Retailers who purchase products for resale without paying sales tax must provide the wholesaler with a resale certificate (reseller’s license).

This document proves that the retailer is registered with the state’s taxing authority to collect sales tax.

If a retailer fails to provide a resale certificate, a wholesaler can (and should) refuse to sell to them without also charging sales tax.

A resale certificate is often the very same document as a sales tax license.

Just like with everything sales tax related, resale certificates and the laws surrounding them vary by US state.

Refer to the post linked here for further details on a state-by-state basis.

You can also read more about Uniform Sales & Use Tax Resale Certificates across multiple jurisdictions.