Am I commingling funds?

[Brett Rhine]

Context: I am house hacking in my primary residence.

Situation: As an incentive to qualified tenants, I have my applicants pay for their own background check and deduct that amount ($35) from their security deposit ($500 - $35 = $465). If they move in I true-up their security deposit by adding my own money ($35) to their deposit account and then return all of it ($500) to them when they move out (less any damages, if any, of course). 

Is this an example of commingling funds? If so, do you recommend that I just drop the incentive? Any other advice on the subject? 

Thanks!