I won't take a holding fee for reasons including your story.
When my property is on the market I continue showing it until the day the lease is signed. I will not sign a lease that starts two weeks or a month out. I have been through the senario in my mind that you describe here and its just dosn't seem to be the best way to do it for my property. (There are so many people interested it just dosn't make sense to sign a lease before the prospect tenant wants to move in.)
So if someone wants to rent the property I tell them right off, if they ask, I will not hold it. I have had people not rent because I would not hold it but who knows if they were sincere in the second place. It is a first come first serve basis. Showing your property on the same day as lease signing is a good way to just keep the system flowing. It is an insurance policy that the property will be rented to the first qualified applicant.
It takes work to prepare the house for showing. More work to answer all the prospect tenants. More work to set up showings. Then finally there is the signing of the lease. If you stop short and do not continue your system of pre screening and showing while you have a prospect tenant being screened you are cheating yourself.
Hope this did come across as rude. Trying to explain a system that I use that I think would work better for you.
I took the security deposit and signed the lease. The move in was in 5 days.
Move in day came and they didn't pay me the rent money! I told them they couldn't move in...BUT..they had a signed lease!
They called the police...yes, I had to let them move in..they had a signed lease. That made them tenants already. Then..on the 2nd day I had to post the 'pay or quit' and go through the whole eviction process!!
Now.. I do not sign the lease until the LAST thing is complete.. walk thru, money paid, utilities cut over, etc.