Just adding my experience with the famous Yaton.
Received 19 out of 20 of my carts. He refunded the 20th (KoF 2000) since he said it wasn't working when he tested it.
The packaging was awesome. Each cart was in an individual bubble wrap sleeve sized for MVS carts and each cart came in its own individual box. Kits are minty fresh--didn't look like they had ever been opened (the cardboard slots where you open the box weren't bent/creased at all).
I haven't checked for bootlegs yet, guess I'll do that next weekend. I think Yaton checks for boots now since when I asked him about a specific game I was looking for, he told me he had the boot but not the original. Also assured me that he doesn't sell boots.
The games themselves were pretty clean, though on the dusty side. I don't really see the need to clean them. A few of the games had dirty/dusty contacts (KoF 95, LB2, SS2, etc.) but after blowing hard and popping the game in and out of the MVS mobo a few times, all graphical/sound issues went away.
Oddly enough, two of the new games I bought had issues. Metal Slug 4 was glitchy on the 2nd Stage boss (graphics got all garbled). Blew air, put the game back in, finished the game without a single problem. KoF 2003 had weird sound (seemed like one channel was cut out entirely) but after blowing and putting the cart in and out a few times, it cleared itself up. I'm not sure whether I should assume that these might be boots, or that the contacts were just dusty or whatever since the games (presumably) hadn't been played before.
Anyway, he gave me a nice discount since I bought so many games from him.
Loose carts: Blazing Star, King of Fighters 94/95/96/98/99, Last Blade 1/2, Metal Slug 2/X, Samurai Shodown 1/2/3/4, Waku Waku 7
Complete kits: KoF 2001/2003, Metal Slug 4/5
Got my games in less than 2 weeks from China and Canada.