I had the sound go out on an X-Men arcade I was selling. Never had any issues before that, but wanted to play a final game before the buyer got there. Called the buyer and explained what happened and offered a discount if they were still interested. They took the game at the discounted price, but I felt bad.
Also was on the receiving end several times. All these games were described as working, but when I arrived they had issues. Hardbody wouldn't start when I arrived to pick it up. We messed with it for about 30-minutes, then I finally just made an offer. Buyer accepted. I can't remember exactly what was wrong, but it wasn't anything major. Congo was completely DOA. Again we messed with it and found a ROM in upside down. After that was reinstalled there was still no sound or video. It was a good deal, so I just paid the agreed upon amount and loaded it up. Put a few hundred into it to get it working. F-14 had multiple issues including flippers, pop bumper, and scoring not working. Seller didn't want to budge, but we negotiated it down a very bit. I wish I would have let that one sit. I brought it 90% of the way then passed it along as a partial project to someone else.