This is just IMHO but I think that's going overboard with ratings. You either make the transaction or you don't - so you either get a postive or a negative.
Opening up a rating system from 1-10 does more to cause annoyance than anything. What's the difference if I rate the guy a 10 instead of an 8? What happens if I do a transaction within 24 hours and someone always online gives me a 5 because I "took a long time?" You're opening the system up to interpetation from different members which in the end makes it to the same point. You're also creating the need for some kind of moderation to make sure that unfair ratings aren't giving out.
You get a negative if you do a crappy transaction or don't follow through on your deals or you get a positive if you do things the right way. I think that's good enough to judge a person on.