I recommend acknowledging the call right away.

We usually check in after receiving their report and fix any minor issues that are listed on it and acknowledge that we know the other cosmetic stuff is there and they won't be charged for it at lease end.   

Yet to run the rental history, but the prospective tenant has acknowledged in my pre-screen check list that he (and his wife) have fallen behind on a rent previously. 

Depending on whether your repayment plan includes an acknowledgement that he owes you $X, you may have to start all over again in court.

If the applicant requests to apply online I email over the application (along with the qualification acknowledgment). 

Okay, first, by her paying the new amount, she has acknowledged receipt of the new lease agreement and she has agreed to the terms - at least as far as how much rent she needs to pay. 

I certainly have reached out to the tenant urgently requesting that she communicate with her neighbor and confirm acknowledgement of the request. 

If you find that their service dog is distracted by you, runs up to you or even really acknowledges you, barks at you or other dogs, shows any aggression or tries to get at food, etc then they are NOT a service dog and they are NOT under the control of their handler and you do NOT have to rent to them. 

@Sue Kelly, yes I have the standard early termination addendum - form RLAUC-1.All my tenants check the first box (the two month termination fee/liquidation damages).Now, I don't think there is any point to choose option 2 "I do not agree to liquidated damages or an early termination fee, and I acknowledge that the landlord may seek damages as provided by law." 

But first the background:- Acquired 3 Flat Building in Cook County  Feb 2016- Inherited Section 8 Tenant with lease expiration June 30, 2016- Rents are deposited via Direct Deposit by the Housing Authority of Cook County- Rent is well below market, I'd say by ~$500 / month - Provided 90 day notice to tenant that I would not be renewing lease- Tenant acknowledged and agreed to look for new apartment- 2 weeks ago, tenant said they haven't found a new apartment yet and requested to stay longer.