Cameron has a great answer.
The Earnest Money needs to be held by a third party as a good faith showing to go through with the transaction. In Washington it is required to be deposited according to the executed contract.
This is a term of the contract during negotiations. You can request anything you like as a buyer or seller. Typically it will be deposited within three business days from acceptance of the offer. However, a buyer and seller can agree to anything that they like - just make sure that you get it in writing.
Be sure you have available funds to cover that check.
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