Bidding on an item with no intention of buying it, to push the price up — by the seller, or by somebody acting for them.
It is the oldest auction fraud there is, and it is the one that would make a live marketplace worthless.
Why it is worse than other cheating
A fake item can be returned. A late parcel can be chased. Shill bidding corrupts the price itself — you pay more, you got what you wanted, and nothing looks wrong.
There is no refund for it because there is nothing visibly to refund. That is what makes it corrosive: it works precisely because the victim cannot tell.
What stops it here
The direct version is refused outright. A seller cannot bid on their own item, buy it, or make an offer on it — the server rejects the request. Can a seller bid on their own items?
One verified number, one account. Which makes a second account a deliberate act rather than a convenience. Can I have two accounts?
It is on the not-allowed list, along with buying from your own store to inflate sales — and both are suspension matters rather than warnings.
The data is visible to Metzee, in a way it is not to you: which accounts bid on which store, how often, and where they stop.
What it is not
A host being enthusiastic. Pace, energy, "this is about to go" — that is selling, and it is allowed. A performance is not a fake bid.
Losing to somebody who wanted it more. The commonest reason a price went past you is the ordinary one.
A maximum bidding on somebody's behalf. That is a real buyer with a real ceiling, set earlier.
Signs worth reporting
The same few names winning everything from one store, show after show.
Bids that only arrive while the price is low, and stop at a plausible number just below where a real buyer would stop.
A winner who never seems to pay, with the item quietly relisted.
Report it under Safety / report someone. You do not need to be certain — you are reporting a pattern, and Metzee can check it against data you cannot see.
Your own defence
A ceiling decided before the item comes up. If a price is being pushed, you stop at your number and whoever pushed it has bought their own item at a price they set.
That defence works whether or not anybody is cheating, which is why it is the one to build the habit around. How to not get carried away
More: can a seller bid on their own items, how do I know a show is not staged, how to raise an issue.