Oh, gee...where to start?
--Colt 1911 (pre-A1) back in about 1982...in all fairness, it was a lot older than I was, and had probably been messed with a fair bit. I basically gave it away.
--Four different Kel-Tecs. In spite of a lot of free parts (and some paid-for-parts, mostly mags), a lot of F&B, a lot of ammo, none of them ever achieved acceptable reliability. Sold each with full disclosure at a significant loss. Strangely enough, my first try at an LCP worked perfectly with all that left-over .380 ammo.
--A Charles Daly 1911. It may have been messed with, but was represented as 100%. I soon learned otherwise. Sold with full disclosure at a significant loss. Are you seeing a pattern here?
--Two Springfield EMPs. By far the worst and most expensive bad purchase I have ever made. The first one experienced every type of malfunction a 1911 can experience, and on the second trip, Springfield kept it and sent me a new one. Wasn't much better, as it made two trips back. I ended up selling it with full disclosure at a significant loss. The new owner sent it back one more time, and I believe he got it working correctly. He offered to sell it back to me recently, and I almost took him up on it...but sanity prevailed.