It can get pretty frustrating at most shops, but there are a couple around here that are well worth checking out:
The Hunting Hut in Belvidere, IL has been a pretty good spot for me. This location has had three operations in the same building, one was there for many years, and over the years I found a lot of nice guns there, some of which I still have. When the longtime owner retired, there was another owner for a relatively short period of time; less than two years. From him, I bought a prewar HD and a Highway Patrolman, both at reasonable prices.
The current owner has been there about a year and a half, and while it is a small shop, he carries a great inventory of used guns. Late last winter, I picked up a beautiful nickel HD, and last Saturday a very early postwar (Ser C63xxx) 2 inch M&P round butt, with service stocks, and a Savage 1907 .32 in just about new condition. I would guess he had at least twenty-five used Smiths and Colts, quite reasonably priced.
Under three owners, over forty years, I have bought at least fifty guns from that location. As far as I can recall, only one was new.