Small consecutive bids under the leader

What it looks like on eBay

• In the bid history, the same masked bidder appears again and again a few dollars apart, each time followed by the leader’s automatic bid.
• The pattern ends when the bids reach the leader’s maximum, and the probing bidder stops.

Why it counts

Probing a leader’s maximum in small steps raises the final price without the prober risking a win. In the UCI dataset, this kind of repeated outbidding was rare among ordinary bidders.

Innocent explanations

A present sign is a reason to look closer, not a conclusion. Common innocent reasons for this one:

• Many bidders bid cautiously, one step at a time, to avoid overpaying. This is the most common reason for the pattern.
• A bidder may simply be deciding how high to go as they go.
• Bidders on phones often tap the suggested next bid repeatedly.

Check it yourself

1. Open the bid history and read the bids from the bottom (earliest) up.
2. Look for one masked bidder bidding several times in a row, each time immediately outbid by an automatic bid from the same other bidder.
3. Check whether that bidder stopped just below the final price.

Read more about shill bidding and how to spot it, or see how Susbid decides a sign is present.