How to request for Sales Tax Refunds
A permitted purchaser – the purchaser of a taxable item or service – who held a sales tax permit at the time they paid sales tax in error can:
A permitted purchaser who did not hold a sales tax permit at the time the tax was paid in error can ask the seller for a refund of tax paid in error or file the refund claim directly with the Comptroller’s office.
How is a business supposed to determine what to charge sales tax on? That depend on the State laws and the nature of your business and the type of products you sell.