Ok I'm gonna toss in my 2 cents worth.
This is a good idea, but like it was posted, It is going to be abused. If a seller is dishonest enough to sell a hacked player, then they are dishonest enough to steal a certification. What is to stop them from going to a good cert. and just copying it and changing the name to theirs and posting it someplace for buyers to see it when clicked on.
I am an admin on a board (
www.pachitalk.com) not altogether different than here, but we are dedicated to Japanese pachinko and pachislo (slot) machines. Luckily our market is much smaller than the mp3/4 market.
We have sections for comments on vendors, both good and bad. If you want to say something about a vendor then you do it in there. Some of our users have taken it upon themselves to send links once in awhile to potential Ebay buyers that link to our forums. Our board is free and if the buyer is interested in these machines they usually sign up.
Yes here there is a blacklist, and a couple of your sponsors have their own sections. What is needed on here is a section for the white list. If you have had a good experience we need a place to put these so they are together, so the newbies know where to find someone they can trust.
On PachiTalk we don't allow vendors to advertise, this way it keeps us kind of pure in a way. We have a small self contained auction area that anyone, including any vendors can sell their products. We found that this will keep us from being labeled "so and so vendor's board".
If you're curious about pachinko or pachislo come check us out.