10% earnest money deposit sounds very high.  If you are inclined to make the deposit then you might speak with an attorney to be sure that you cover yourself so that you don't loose the entire amount for some reason, like not securing financing or perhaps negotiating liquidated damages at a lower amount if you decide to back out.  Also, state law might limit the amount of earnest money and damages.

That is a large deposit but they can ask for it.  But definitely speak with an attorney and make sure the contract has an out clause where you get your money refunded.

I find it odd they would want that big a deposit when the real estate market is flooded with homes for sale.  Seems like a good way not to get a buyer.

Certainly a Realtor can ask for a 10% earnest money deposit----but I'd be suspect.  Unless this some true million dollar property, don't do it.  You might up end losing the whole thing.

short answer = yes

how badly do you want this house?

The seller and realtor can ask for that, but with a convincing pre-qualification or pre-approval letter, that could probably be negotiated down to 3-5%.  It sounds like you have a frustrated seller that has already had a couple of contracts not make it to the closing table due to financing issues.  To insure he has a buyer that is going have the down payment, he is asking for it right up front.   

In CA deposits are generally 1 to 3 percent of the sales price.

Buyers  who put more usually  sign a liquidated damages clause that limits the seller to 3% of the purchase price as damages in the event of default.