I've had at least 2 brokers say that they won't take an offer to the seller UNTIL I send real deposit money, 10%. Some here have said they negotiated first and then backed it up with 10%. HMMMM.
I've read that some buyers put a time limit with penalties for returning the deposit. If at any point you cancel the deal for legitimate reasons spelled out in the contract, the broker has 5 working days to return the money. The penalty is $100/day after that! Makes sure you get the money back in a timely fashion. Some brokers will hang onto the money so they have you on a leash to keep the negotations going.