I hate this argument because it shows just how little people know about gun laws.
It's federally illegal to buy a pistol outside of your home state. You can't just go to a gun shop the next state over and buy a Glock 17.
For long guns, the seller must follow the laws of the state in which it is sold AND in which the buyer lives.
When I sold guns and someone from New Jersey wanted to buy a rifle, they had to produce their New Jersey permit and I to do the New Jersey background check and waiting period on top of the NICS background check required federally. I had to reference New Jersey laws and could only sell guns that were legal in that state.
We had a spreadsheet we kept up to date with every firearm we had in stock, new or used, listing whether it was legal in each state.