Get the criteria or buy box and keep that buyer in your contacts 

(Both that you know about now and that you are told about form your buyer’s inspections.)Most buyers are going to discount their offer by double what they think it will cost to repair what they can see plus the “mystery repairs” you’re hiding with your as-is sale so you will make much less on the sale. 

He’s also got the porch full of boxes of things they don’t have room for in their unit.

There is an old joke: you don't have to run faster than the bear, just faster than your friend.There are hundreds of leases signed every week, your apartment needs to be more attractive than 50% of what's out there and it will be rented quickly.So you'll have to do some mystery shopping and (ideally) physically look at your competition.

Do any of the properties not fit your Buy box today?  

I agree, something to 'set apart' seems to be the name of the occupancy game aside from location & views...that "Instagram Moment" - theme/mural/badass outdoor space/something outside of the box/really cool game room...just some ideas. 

A general maintenance tech or handyman may not have the expertise to certify a leak that is especially mysterious. 

thats a mystery to me.

They could have come in with the moving boxes, which is the most likely culprit, but they could have snuck in some other way.My lease says I will deliver the home pest-free and handle any pest treatment for the first two weeks in case we miss something.

This is clearly a shakedown, and while I'm not a lawyer and wouldn't know what law it violates, it certainly must violate one or more laws to purposefully conceal what the correct address is in an attempt to have the LL violate housing laws, and thus profit from it.I would request a freedom of information act request, and ask for all documents related to the previous 80 cases, as there are bound to be common themes, such as "attorney claiming to have sent a letter", but all 80 landlords mysteriously never got a letter.