Holding deposits for apartments - Venmo is a No

[C Rutherford]

After showing a renovated vacant apartment 2 weeks now, and getting a seemingly neverending string of high risk applicants... crime records, alcoholics, people with drug issues, evictions.... Orders of Protection, no rental history. Shaky or absent income. A herd of destructive pets, and on. And after watching one after another tenant who checks out good flitting off, never getting back, or changing their mind.

I finally get someone who says they like the apartment and looks like a good prospect.  They work close by they say, and they are familiar with the neighborhood.  They're pleasant.   They fill out an app, and they have enough income for the place.   All this points to a successful rental.  I'm all ready to go ahead.
So, I recommend the Holding Deposit.   In our case this is the Security Deposit amount, which we take in exchange for a form they take with- we keep a copy--- saying they have the apartment reserved pending backchecking.    This gives us time to do the backchecking so they don't just flit off to the next place and change their mind in the meantime, and they have the apartment reserved.

I've been telling people that the Holding Deposit is fully refundable if they don't get the apartment, if they do get it becomes their Security Deposit.  That seemed fair.
This time, however the prospect that looks good and likes the place says they want to put down a deposit to reserve, but they can't get to the bank until tomorrow.

Why don't we try Venmo?  Is my sudden epiphany.
I may be GenX and behind the times, but someone recently got me set up on my phone, and all the young people are doing this.   "Sure!" comes the reply.   Click click punch, and proof of the Security Deposit cyber transferred is right there, and transferable on to the rental account.
We fill out the forms, and off they go.  Apartment reserved.  Now we have time to backcheck.

Or do I?
I hadn't even been home long enough to text the applicant a thanks we will be in touch, let alone check anything because nothing is open until the next day.   When my phone has a notification:  "Deposit Refund Requested".
Apparently, the person saw some place they liked better, wanted more time to think about it and on.
I get a text confirming that.   Waffling, wants to look around. 

It was a disappointing night to be sure, but this applicant was wanting to reserve the apartment until the 29th, move-in date.  That would have been two more weeks with that holding deposit.  What if I had held the place pending with the deposit all that time, and they backed out then?

First, what good is a holding deposit using Venmo especially, when they can just cancel so easy, anytime?
That's like no commitment at all.  They don't even have to make a trip to the bank to back out, they do it reclining in a living room sofa chair, anytime the mood strikes as easy as clicking a TV remote.
Second, what good are holding deposits, if there is no penalty for backing out of them.   I feel as if this is unfair to the leaser.  
We hold the apartment, miss out on other prospective renters, do all the backchecking work then get nothing when the prospective tenant finds something better or changes their mind, and the deposit is returned.
Is there any better way to do this?