QUOTE(mattcam @ April 8 2008, 06:51 PM)

Adam, what document do you show the pimply-faced kid at Best Buy to avoid being taxed?
Here comes a long post*
They should have the document for you to fill in with your State Tax ID number and name, etc. In practice, they don't know anything about that. They
should be able to ring it up as tax exempt as long as they have your ID number. In practice ... well, you get the idea.
Usually a manager will know how to ring it up. But it's a real pain (in their mind) so you sometimes get someone who plays dumb -- especially if the store's really busy. Your best bet is to talk to a manager first and make them do their job. There is some paperwork to fill out. If it's not a big purchase I sometimes just pay the tax so I don't have to deal with it.
At the Apple store (here in Columbus), once it's filled out, your business name goes into a binder that they can look up each time. At Jo Ann's Fabrics, they give you a little card so they can just punch in a number and have your info come up. Michael's and Hobby Lobby are the same way. At Dick Blick, they just need your number to punch into the register. Staples, on the other hand, doesn't do it how they're supposed to, and makes it so much of a pain that we either just pay the tax or buy that stuff elsewhere. At Staples (for us) it's only for CDs or DVDs that we resell. Most of what we get there we do pay sales tax on (like office paper or toner or copies).
Most other places I purchase stuff from is used to dealing with resellers so it's not an issue. At Midwest Photo, I just tell them the name of our company and it's taken care of. It seems they have a different cashier every time I go in there.

With us, if we're selling to a tax-exempt entity like a school or a church (or a large company that pays their own tax -- don't ask, it's complicated), we just take their number down and there's a place to put it in our accounting software.
*Now, this is all for Ohio -- I can't say anything about other states because I have no idea.