If it does't rent out and tenant doesn't pay, you can put it towards rents due and actual damages, but I don't believe it can just be forfeited. 

Once they sign the lease, the deposit will be forfeited if they change their mind.

I've kept 3 deposits because people move before 4 years and forfeit their deposit. 

Why not just say so and forfeit the security deposit?

I have ( I should say had) a potential tenant she past the screening process says she doesn't want the apartment for another 30 days (July 1st) ok no problem I said I wanted a security deposit = (to 1 months rent) if you decide after the 30 days you still want the apartment I return your deposit and you are still due me 1st month and security deposit to begin lease agreement. if after the 30 days you decide you don't want the apartment you forfeit your deposit. and we move on ....is this fair?.

The IRA holder is also forfeiting any compensation to avoid self-dealing.

There is a key turnover receipt that I have had some tenants sign in the past which documents that they are forfeiting rights to the property and they left the keys plus signed receipt in the unit without ever directly meeting us but this was more of a precaution than requirement for us.

We also typically have a contract clause indicating in the event any of the rents are late, the vendor forfeits any claim on the uncollected amount - essentially, if it becomes our problem, its our revenue.  

Here you have to have deposits in their own separate account and not comingled with personal funds or you forfeit your right to hold from it. 

Binder deposit which will remain as a binder until closing, unless sooner forfeited or retained, according to the provisions in this Agreement. $________________ B.