Scam? Yep.
Bid directory owners will never see it as such, but yes, bid directories are nothing but a scam.
What is a bid directory? A bid directory lists sites based on the amount bid, with the highest paying sites listed at the top of the list. The top bidders are also listed in order of bid amount on the front page (where every one can see just how big of an idiot you really are).
This directory model doesn’t list sites based on merit. Quality content? Doesn’t matter. Timely information? Doesn’t matter. All it takes is a little ignorance and willingness to part with your money.
Many bid directories are placed on recently acquired deleted domains with foolbar PageRank. It’s easy to identify the scammers on popular webmaster forums peddling links based on the Google PageRank of an unrelated domain. The domain name itself should be the first indication that someone is looking to profit off of the ignorance of others.