I'm doing a podcast episode on the original Silk Road and wanted to make sure that I get this point correct. I know users could rate vendors and give feedback, but I never had the chance to talk to a vendor to see if there was a reputation system for rating buyers.
While it is true you couldn't rate buyers on the site, concerns about buyers and scammers etc were shared among vendors on the vendors round table on the forums. Vendors would also compile, and some share, buyer blacklists.