Pinned means the barrel is pinned at the frame to keep it from turning loose. It is not done these days. You can see the pin just above the barrel on the frame. If you do a search on the forum, you'll find lots of information about it.

Recessed means the cartridges fit flush with the back of the cylinder. If you look at it, you'll see what I mean. This also is no longer done. It allowed for tighter tolerance at the barrel/cylinder interface.

As far as what to look for, primarily you want a tight lock-up when you put it in single action mode, little to no end-play on the cylinder, no signs of significant dents, marks, etc., which would indicate dropping or other abuse. Again, you can look up what end-play and lock-up mean on this forum. Others have described them in detail in earlier posts.

Typical model 28-2, if used, would show signs of wear from holster, etc., but number of round counts can be hard to determine. You want it to be clean and tight. The price would be ok on one that is. I'm sure you'll get some other responses. This is a great forum for S&W revolvers.

Hope that helps.

Oldgun