Itinerant Salesman Question

I can't speak for all states but here in Pa. it's where the customer is and where the sale takes place.
Let's say you are from Ohio and I buy something mail order or internet in Pa., no sales tax need s to be collected.
But if you're at a gun show in Pa. you need to collect taxes.
Pa doen't like not getting their taxes.
Ask me how I know.
BTW, we are avid gun people here. NRA loves us.