Although purchasers generally bear the actual economic burden of paying sales taxes, the administrative responsibilities for collecting, reporting, and remitting the taxes to the appropriate tax authorities are generally placed on their sellers. As a practical matter, from your perspective as a purchaser of taxable goods or services, your sales tax obligations pretty much end once you have an invoice or receipt showing that you paid the tax to the seller. This is not meant to imply, however, that you don't have other sales tax concerns as a purchaser.
Exemptions. Perhaps your biggest sales tax concern as a purchaser is making sure that you don't pay tax on purchases that are eligible for an exemption from tax. This entails identifying the exemptions to which you may be entitled and then preparing the exemption certificate that you must provide your seller to receive the exemption.
Use tax. If you've made purchases upon which you didn't pay sales tax, either because the seller just failed to collect the tax or because you claimed an exemption, you should also be concerned that you eventually may have to pay a use tax on the purchased item.