dpd1 - 5:50 pm on Apr 15, 2013 (gmt 0)
Most businesses know how negative people are about paying a tax, and that it is likely people will do exactly what you're doing, and buy from someone else... Therefore, they know it would most likely be in their best interest, not to have to charge a tax. So that in itself would probably indicate that it's legit. I myself actually pay people's sales tax each year, because I know how strongly people feel about it, and I know that if I charged it... I'd probably lose more money than if I just paid the tax. I'm not happy about it, but I have no choice really. Just wish they'd come up with a standard nationwide, so people don't have to keep going trough all this.
That said... I don't think it's out of the question for a business to genuinely not understand tax laws. I personally have met accountants that pretty much don't have a clue, and instruct their clients to play it way too safe... paying for stuff they don't need to pay for. Some accountants are very paranoid and basically just want to protect themselves, more than anything.