California Short Sale-Agent wants deposit?

[Alisha Weeks]

Hey all-
My husband and I are currently trying to buy our first home in Southern California. We found a short sale and put in an offer at asking price. The sellers accepted our offer. I'm assuming the offer is now on its way to a negotiator or bank (hopefully). The thing is that the seller's agent is now asking for a deposit. He claims that if we give the deposit he will list the property as pending. He says that even though the sellers have accepted our offer, if another offer comes in he must submit it to the bank also. I guess he will list the property as pending on the MLS to detour others? Our agent was not too sure about this which makes me nervous. My questions are: Is this something that occurs often? Also, even though the sellers have accepted our offer, they can accept another offer to be submitted to the bank after ours?
Any insight or advice would be very helpful. Thanks