I sold a "D" model SKS for $50 profit and a Romanian AK for $50 profit.  Later, just before the end of the show I was looking for a model 19 Glock. The one I had spotted on saturday had sold before I got there sunday.  Well I overheard this guy trying to trade his 19C and the dealer offered him $375. He was unsure of what to do 'cause that was going to leave him a little short for the purchase he was going to make.  He eventually let me take it for $410.  I immediately took it to TR Grahm (well known Glock armorer) and had him tear it down and evaluate it.  I knew it was pertty good because the gun was very clean with no wear marks/box and 2 mags.   TR determined that the gun was a 2001 manufacture and most lilely had only a few boxes of ammo through it. He said what I basically got was a brand new gun for $100-1
$150 discount and no paperwork.  :)