Are Dealers Supposed To Collect Sales Tax At Shows?

Most state tax depts may presently be staffed too thin to have agents to monitoring shows the way they did 20 years ago, but you can bet they still troll the big shows in places like Boston, NYC, DC, Chicago, New Orleans, Dallas, Las Vegas, San Francisco (to name just 8 out of a much bigger list), etc... The big cities with the big tourist/vacation/convention centers that host the big shows still draw the revnooers out of the woodwork like ants at a picnic.

The state tax depts may not presently have the horsepower to cover small, local shows like they used to, but they're not extinct yet. They're like cockroaches. They'll drop back and lay low when they have to, but they'll survive anything and as soon as the conditions are right, they'll repopulate and be back in force that'll blow your mind (unless the Mayans are right---in which case we'll all be done paying sales tax two weeks from yesterday).

It most certainly is a state by state requirement. I remember not that long ago a state considering implementing it, and going back and forth on the legislation. I don't remember the outcome, as it was not a state I do business in. I imagine sometimes some sales are pocketed, but I prefer to consider them as paying taxes on sales out of the price. If they choose not to, I am not aware of it.
Reading through the posts here I noted someone mentioning NJ, and that they were unsure if NJ had coinshows still. NJ still does host coin shows, just as a point of information.

They are suppose to, BUT if they do they should give you a written numbered receipt. I always ask for one when they charge me tax and they must provide it.