For Sale By Owner- please help!?

We are selling our Mom's home on our own as she ped away. We have an offer that is possible, but our attorney is away this week to consult- The prospective buyer has asked us not to show the house to anyone and have a handshake contract now and he wants to go in the house and start drawing plans to expand the home but he has ignored our request to make a deposit on the house- I do not think it is appropriate to let him do this without anything signed. And I do not think that the house showing should be stopped for a 1000.,00 deposit- Our atty said he should put up 10 percent. Any ideas on this deal? Thanks.