Let them move in with a deposit and first months rent. 

My buddy sold for ~$500k over its existing use value and no contingencies and did not even convey existing tenant’s deposit.  

A good property manager can help with tenant screening, enforce lease terms, and handle evictions more efficiently if it comes to that.Require a Larger Security Deposit: Within the bounds of local regulations, a larger deposit can provide a cushion in case of damage or unpaid rent.Consider Rent Guarantee Insurance: Some companies offer insurance products that can cover lost rent in case of tenant default.

Consider all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

It is common for rental property investors to feel the pain when a property turns over but keep in mind that is why we retain security deposits for you. 

Once you win the auction you have to put down a 15k deposit so I don't want to not have a chance of getting it back.

Payment TermsContract Value: $[Insert Amount].Deposit: $[Insert Amount] due before the commencement of work.Payment Schedule: Payments to be made as follows:[Milestone 1 and payment amount].

If they pass the screening, also find out who is paying the deposit as that is the person you will be returning it to once they leave.

But they auto-deposited $50 into my "marketing account."

Earnest Money DepositAnd if you want to cover all your bases, you can also consider saving for an earnest money deposit (EMD).