in GA
sometimes there is a sales tax
sometimes a buyers premium
sometimes a deposit
every auctioneer and storage facility is different.
As for me I pay the tax if they want it.
but sell my stuff at yard sale and flea market
If I had to keep up with taxes I'd go back to a real job
Legally, we are responsible for collecting sales tax and paying it to the state regardless of whether we sell in a store or at a yard sale/flea market. The only time we wouldn't be required to collect sales tax is if we are selling over the internet to an out-of-state buyer.
edited to add that we also wouldn't collect sales tax if we were to sell an item to a registered business which is going to resell the item (and has a reseller cert), since sales tax is only paid by the end user.