Simply write a check from one to the other and make the deposit.

I don't put up any earnest money deposit  so no risk.

You require your t/b to place a 5k or 3% (whichever is greater) option deposit on the property (aka, your profit in the deal), and add that into the price of the property.  

If there is, pay the bill and deduct the amount from the security deposit.

Step back a bit and figure out if you want a turnover there right now, if they have paid timely and no complaints during their lease term (last owner should have given you the deposit, applications, any leases they signed for him, rental history of late payments, etc.).  

Do not let them just give up their deposit in lieu of last month rent.

Make sure you have the terms clearly specified in the purchase contract including the Earnest Money Deposit amount (payable in 3 days from signing the contract and fully refundable if you don't remove the contingencies), an appraisal contingency, a home inspection contingency and a clear title contingency.2.

Is it your business policy to accept security deposits in installments? 

I do have a substantial security deposit, and a *previous* landlord apartment building, not where she was living when I accepted her application, said she was a good on-time paying tenant who got her entire security deposit back, and I did spend 45 minutes at lease signing reviewing the terms of the lease.I did read the entire ,”Would you start eviction over $50?

You can always ask for two to three months security deposit also.