The deposit is required in CA in order to make the agreement a contract. So, technically, your deposit can be $1. That being said, Sellers look at the deposit as a measure of how serious you are as a Buyer. Some will tell you to put 3%, but there is no hard and fast rule.
Consult your agent for advice as to how best to construct your particular offer. I usually ask my clients to put at least 1%, but every situation is different.
Please be sure to know your rights as they realte to contingency periods, arbitration, and liquidated damages too!
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