Was looking at cheapo shotgun in Pa. Walmart (York) and was told it could not be sold to Md resident--must just be Walmart rules -wasn't going to argue with the guy.
A few places have that policy, being the laws of both states must be followed, it must simplify things where a big box store doesn't go to the expense of training their people on the intricacies of law. There are several good gunshops in the area though that do deem knowledgeable employees and service to out-of-state customers worth the trouble.
Posted this before: 5-6 years ago, stopped in a WalMart in Florida and the salesperson was a retired school teacher from MD. Store was slow, therefore we talked for a very long time and got around to selling me a long gun, he flipped the screen around and showed me the company policy selling to MD residents NO-GO!
I had that happen when I lived in Maryland. I went to a WV walmart, and they had this rule that they would not sell any rifles to Maryland residents. They said it was the store policy.