Get used to seeing more of this. The states are desperate for more revenues, so they are getting far more aggressive in enforcing their sales/use tax rules. Basically if the seller has a physical presence in your state, such as a store, a warehouse or an office, they are obliged to collect sales tax from you to pay to your state.
This is not to say that some crooked sellers may not pay the taxes they collect from you over to the state. This is called tax evasion and often results in jail time when they get caught.
This is not to say that some crooked sellers may not pay the taxes they collect from you over to the state. This is called tax evasion and often results in jail time when they get caught.