Mahonri, I agree with you completely. When it comes to buying and selling, it feels better to buy from someone who has been posting here for longer (says the person with only 100 posts). This spreadsheet would be very nice too, however, I would recommend having to sign in through BYC to make comments. That way the seller can't give themselves lots of positive feedback.
Other (very minor) comment is on the rating system. People typically think of 1 as being the best and 5 being the worst, at least I do. Maybe consider switching these numbers around?? Or go to a 1-10 scale, where 10 is best? I don't know, but I thought that the people on there had lots of bad feedback already... oops. Maybe it's just me....