Your agent should be familiar with the SSA (short sale addendum) document. That document shall specify how you want to do things. You can indeed submit a deposit, you can hold the check uncashed. There is NO SET ACTIVITY, by law. You can do it anyway that you want. If you want to convey seriousness by advancing money you can do that. If you are a backup you are a backup no matter how you slice it. The bank doesnt care if you have submitted your deposit to escrow yet or not.