Ive bought very few used games that Ive had issues with, 2 come to mind though.
1. Bought HDN2 only to realise the disc inside was for HDN1 -_- Easily got it swapped though.
2. Bought FFXII only for it to freeze, thankfully it was within the first hour of the game. Got it swapped at an EB Games despite not buying it from them, knowing a manager has its benefits

Buying the same game twice used cause i didn't remember I already bought them used... Darksiders, Armored Core For Answer, Armored Core Verdict Day, Prince of Persia.. -_-"

Bought Mass Effect 3 used for the 360 and it comes with 2 DVDs.

The first DVD was perfect. Everything went smooth, no problem whatsoever. When I get to the point that the second DVD is needed, thing crashes. Console can't read the disc.

And it was too late to ask for a refund at that point.

Had to purchase a second ME3 copy and, while this time it worked, the second DVD was all kind of craziness. Bugs, glitches, heavy stuttering, and an insane amount of problems. First DVD, however, had none of the above. I beat the game, eventually. But while I didn't find the second copy that bad (as the craziness, at times, was too funny), the first one burned me bad. It was a major turn off, really.

Another experience was with Dead or Alive Xtreme 2. Not very interesting, but first disc didn't work. Bought a second copy. Second copy freeze every single time the game boots for the first time. Bought a third copy. Console refuses to read disc. Fourth copy? This one finally works. Some weird shit here.

Hahaha Ive also done that before, I was so excited to get home and play and then wondered why I already had a save file -_-

Wow, really you two?

I've bought several used games. I stopped having problems with them when the PS3 came out. Blu-ray discs seem to be more durable than old DVDs.

Don't think I've actually had a bad experience with used games, granted I don't buy many used in the first place.

Not this negative Nelly.

My copy of Ape Escape 2 wound up being a copy of horrible party game Ape Escape Pumped and Primed.

On the flip side, I was reading posts on a little known site called "VGChartz" and was that the exact same thing happened to somebody else! I made a profile just to say "Hey, that happened to me, too!". The rest is history.

Very few bad used game experiences for me, but my first foray into used games was not great. As a wee child I stuck $10 in an envelope and mailed it to Funcoland for Dragon Warrior on the NES. I finally got it, was delighted it both worked perfectly and was an honest-to-God RPG (a genre I hadn't played before). But then I found out the save battery in the cartridge was dead. Many years later I would have known how to fix this, but back then it was insurmountable. I tried to just plow through it in one sitting a dozen times or so, but I couldn't do it.