Perhaps the most talked-about of the various invalid strategies. Shill bidding is the act of bidding to deliberately and only raise the price of the item. Often, but not always, this is an act of collusion between the seller and friends, who try to get their buddy a better price. Sometimes, a seller will bid on his own items through other id's. The most easily recognized form of this is when somebody makes a huge bid, exposing the current leaders proxy, then retracts and bids just under it. Other tactics are more complex, often with rings of people helping each other out. Shilling often results in expulsion from eBay, although it is very hard to prove.

Lone Gunman shilling is a supposedly altruistic, albeit perplexing, style of bidding. As far as I know, only the king of small price engages in this style, assuming he's telling the truth. A Lone Gunman searches auction pages. If he finds an auction where the seller, in the opinion of the Lone Gunman, is getting less than a fair price, then he will bid one or more times until he is satisfied that the seller is getting a price that meets the Lone Gunman's approval.

The Lone Gunman will often claim that he's not shilling, and say that shilling is only the result of collusion between buyer and seller, although this is completely contradicted by eBay's rules. Until a court of law rules otherwise, shill bidding on eBay is exactly what eBay says it is, and the current rules do not say that shilling must be the result of collusion.

Lone Gunman Shilling is odd. One the one hand, they claim the high ground and they claim that they are interested only in the pursuit of fairness. However, their actions will often result in one of two things. They will either win the auction, preventing somebody else from getting an item that they wanted, or they will force the bidder to pay more. As for the second option, which is the main goal of the Lone Gunman, this may be fair for the seller, but how is it fair to the bidder?

It's not the job of somebody else to determine what is or is not a "fair" price, and it's not anybody's role to artifically inflate prices. "Fairness" does not mean forcing people to pay as much as possible.

On eBay, there are chat boards where members exchange ideas, questions, and a great deal else. Often, some of the discussions can get quite heated and many times hurt feelings are the result. Sometimes, a person who gets angry or offended at a post will seek revenge on the person that caused the insult. They will follow the person around eBay, bidding on everything they bid on, seeking either to prevent the bidder from winning or forcing them to pay as much as possible. This is much like Lone Gunman Shilling, but with a different focus. In this case, the Enemy Bidder is specifically targeting one buyer in particular.

In response, many people have posting id's that have no relation to their buying id, and of course sniping is a great defense against this tactic.

The act of bidding on a sellers auction only to leave them negative feedback minutes later.

This often happens as the result of bad blood between two people. The offended part seeks to "get even" with the seller by ruining their auctions. Arguements on the chat boards are a common source of this, and this is a large reason why so many people have posting ids. Of course, hard-core anti-snipers claim that this problem does not exist, but they're just showing off their ignorance.

Since this hostility is directed at the seller, sniping cannot really defend against it, unless you bid more than the bomber, in which case the bomber will just bid again on another of the seller's auctions.