Care to share the info he gave you?
Something about carefully removing the metal that was spot welded to the battery, then using a magnifying lens to make sure he gets it as perfect as possible, he grinds out the solder marks ONLY until it's smooth and flat, and no more than that. Apparently some other people who were selling these batteries were grinding the hell out of the positive and negative connections to the point where there's 0 evidence of the solder marks, which is both unneccesary and dangerous because you'll remove too much anti-corrosion plating and most likely weaken the metal too much to the point where it will break. Anyways i'm somewhat sceptical, but worst case my regulated mod doesn't fire it or they underperform and i'm out $20. It seems like he knows what he's doing though, and has sold a lot of them and I haven't seen a single negative review or anything. Also have seen people on reddit buy some from him and said they were fine. So here's hoping, I suppose!
Edit: Forgot to mention that its normally just the positive connection that needs smoothing out, apparently the spot welds aren't usually as bad on the bottom of the battery and don't always need smoothing!