If properly looked after, a mere 500 rounds per barrel is a trifle for a big-bore.

Just examine the thing properly if you can, and rejoice in the fact that it has been exercised frequently by the previous owner. Not sure of their retail in the US but that sounds like a decent saving on the new price.

Hell, my favourite double is 77 years old and has probably had quite a few thousand rounds down the barrels, a couple of thousand while in my custody. Bores still look like new.