|Re: eBay sure is a crazy place...|
Message #12 Posted by megarat on 31 Aug 2007, 2:34 p.m.,
in response to message #5 by Randy
> After all, how hard is it to compare IP addresses?
Unfortunately this wouldn't work. Comparing IP addresses would create heaps of false positives, as there are many, many major providers that represent thousands of users with a single IP address, because of their router/firewall topology.
I would be quite upset if I placed a last-second bid on a beloved item, only to have eBay's shill-bot reject the bid, simply because the seller (or another bidder) and I shared the same ISP.
While I haven't given this much thought, the only meaningful way I can envision to sniff out shill bidders would be to (data-mining style) run some comprehensive queries on all the auction data, perhaps via machine-learning algorithm. For each auction, note the seller, the bidders, and probably some other behavior (like the bid increment amount, and time before auction close), and do a full comparison. The shilling IDs would (hopefully) be visible through bids on multiple auctions by the same seller.
Even so, this still wouldn't be perfect ... in an eBay niche like vintage calculators, people bid on multiple auctions by the same seller all the time, so you'd still get false positives, even if you use a smart-ish distinguishing criteria. I expect that there would be some obvious true positives, possibly by bid volume or other behavior, and perhaps public enforcement of these cases would scare everyone else straight.
Alas, this type of analysis isn't free, and since eBay stands to benefit from shill bids, I can't imagine they'd bother with something like this, unless the reputation of their marketplace was seriously at stake.
Still, it's a fun mental exercise.