How to determine if a company is forwarding their sales tax?

Brad asked:
I purchased a fairly expensive piece of equipment from a company over the Internet that in the description of the item claimed sales tax would have to be paid in several states including mine. I was fine with this except for in the end, they charged the wrong tax amount (3% more than my [...]

What affect does Internet purchasing have on local governments and sale tax revenues?

Cotton Eye Joe asked: Do you ever feel guilty that you are buying something out of state for tax free?