Many of us choose to have a professional prepare our taxes, so we are not aware of the nuances in the sales tax laws of each state.

As part of the tax preparation process, your paid preparer should be asking you if you have any sales/use tax to declare for out of state online purchases if your state has sales/use taxes...they cannot answer the question on the return forthrightly without asking you that. You may not know the answer, but they have to ask if it's on the return. Tax preparation software that many of us use to do our own taxes also asks the question as do the paper forms for most, if not all states, that have sales/use taxes. The issue has been in the press quite a bit over the past few years as new regulations are passed. So I'd contend that for "most folks", there's little reason for them not to know about it. As in all things about the law, not knowing the law does't release us from it, either.

But yes, it's absolutely true that most people do not keep track and remit. That's why many states are now requiring (legally enforceable) that out of state vendors who's revenue from their state exceeds a certain amount must collect and remit sales tax at the state's rate for purchases by residents of their state. PA requires that now, by example. I suspect it will not be much longer until this becomes universal and that the only thing holding it back is the complexity that it poses for small business software to be able to track, maintain and remit sales/use tax for the over 3000 individual jurisdictions in the US that would apply.