I don't know how any of the big boxes deal in English (or Damascus) guns without having a good set of tools on hand to measure barrel wall thickness. It is my understanding that most do not.
I agree. The store here does have a Manson gauge, although I wouldn't know if anyone knows how to use it. I'd say your statement applies to pretty much any vintage gun, and not just for the big box gun stores. I didn't even know a barrel could be honed out until about 4-5 years ago. Now I'm looking for it 100% of the time. Another local shop threw a couple of my guns up on consignment without ever taking the first measurement. I guess it's "Buyer Beware" every where you go.