People keep backing out! What is your process?

[Jennifer Rysdam]

I keep getting these people who want and qualify for an apartment but can't move in until 2 weeks from now or whatever. I collect the nonrefundable retainer of $250 (half of deposit), and then at the last minute they back out. So, when do YOU have people sign the lease? Do you make them do it now if they aren't moving in until 2 weeks from now, or on the 1st? What is your process? Thanks much!