Booking deposit

I am selling my house in a private deal. I have an EA working on selling for me but I was approached by someone interested in buying and am due to get back to them with a price this week. My expectation is that they will accept my proposed price.
One question I have - what is the normal amount of booking deposit ??

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5K, usually subject to contract, which means either side can pull out before singning the contract. When signing the contract 10% of the purchase price minus the 5K booking deposit is standard.