I've seen a couple less than honest shops doing that with used glocks. Pulling the extra mags and marking them at $45 and trying to sell the gun with only one mag, at above new price.
These are also the same guys who still have .223 in stock because they have 20 rd boxes marked at $22, and bare basic bushmasters for $1,500. I'm a capitalist, but greedy, dishonest, capitalists give us a bad name.
I won't buy anything from shops like these.