Part of it is the total number, not just the percentage. In your case, 117 is a fairly high number of auctions, but enough that 2 negs screw the numbers. If I got a negative, I'd probably have a 90% or so, just because I've bought such a small amount of stuff. This dude had about 3-4000 auctions. So 98% is much more significant.

I am the Doctor, and THIS... is my SPOON!