Legal Question in Real Estate Law in California

It is legal for third parties to make offers, but the seller cannot accept them if the seller is in a binding contract with you.

Mr. Roach is exactly right. If you have a signed contract, the seller can take other offers to keep "in the pocket" in case your transaction falls out of escrow for any reason, but otherwise if there is a valid signed offer and acceptance it is binding on the seller and if she backs out you can sue for damages or even to force the sale to go through.

It is certainly not illegal to make an offer on property where another offer has already been made and accepted. However, once a seller has accepted an offer, the seller cannot legally accept a subsequently-made offer. Note also that with real estate, both the offer and the acceptance must be in writing to be binding (well, usually at least!).

IF you have received from the seller a fully executed written unconditional acceptance of your purchase offer, then you have a potentially enforceable 'contract'. If you didn't get the seller's unconditional acceptance of your offer, they are free to accept any other offer they want. Real estate agents and brokers understand the process, that is what they get paid for in representing you. If you are doing this on your own, you will need to learn the process rules and procedures yourself.

Even if you have an enforceable 'contract', the sellers are free to take any number of 'back up offers' on the property, in the event you fail to comply with all the contingencies, terms and requirements of your 'deal'.