In recent years the housing market has been so competitive that escalation clauses are often written into offers. They typically include a base offer of $X and then an agreement to escalate that value by increments (maybe $1-5k at a time) up to some cap. All the offers are collected by a certain date and then an auction is run behind the scenes by the realtors involved.
What's to stop a seller from having one of their friends enter into one of these escalations? Submit a non-serious offer with a high escalation and include a minimal deposit which would be forfeited if that fake offer happens to win but otherwise hope it comes in 2nd to push everyone else's escalation up.