If done right it can work but if you come off as a jerk they may cut off there nose to spite their face. The most effective one I pulled was a $15K credit the day before contingency removal about 2 years ago. It worked even in a hot market because I figured out the sellers were set to close on a replacement property in 2 days and knew that they would be able to keep the buyers deposit(10K) if they walked after contingency removal. Theyw ere pissed but they did it cause I had them over the proverbial barrel.