I wonder what would happen if you 'broke' in (got a locksmith to change the locks) while they were out and said the same thing? 

Also, since it hasn't yet been mentioned, once he's out and you have the keys have the unit quickly rekeyed. 

We are looking to convert to a smart lock system to help reduce the cost of rekeying, time wasted locating keys, and travel time.

When I got the statement , rent is missing for those 20 days and property manager is charging the landlord for new leasing fees, advertisement and re-keying and the reason PM is giving is there is no fund left in the security deposit, so PM is charging the landlord. 

They could take that lease and sign it and show up and get a locksmith and move in. 

For my multi, I've used the kwikset smartkey system and easily rekeyed after a tenant leaves (takes less than a minute).

I'd love for it to be a low-management system, dead simple to re-assign or "rekey" fob/card/phone tenant access to units based on lost devices or occupancy.

They have what are called "Marks" locks on the doors and it's expensive to replace or rekey. 

Use high flow toilets, snake the plumbing, replace the water lines that drain to the sewer if they are old, tile or cheap/sturdy laminate, Landlord Locks, or easy to re-key locks and get them solidly rent ready.Work with a few realtors to list your property, but once they past the sniff test, i.e., 3x rent as income, no current collections, etc., etc., then I interview them, get to know them, ask any question that comes to mind and make sure they completely understand that I want my tenants to love their home and feel totally comfortable, but if rent is late, I will never waive late fees (but I have twice for circumstances that required flexibility) and I will evict at the first sign of a problem.

If there is no one and she has not moved in yet then I can go ahead and rekey the lock which i did.