If a tenant locks themselves out, I have a spare to sign out to them or I can go open the door (there's a fee, but it's cheaper than a locksmith).If I sign out one key and it hasn't been returned yet, I still have a second in the office for an emergency.

There is the old story about a driver who locked his keys in the vehicle and had to call a Locksmith to open the door to the vehicle.

Make sure you get the doors rekeyed as soon as she moves out.

If the tenant isn't available to let them in, I need to call a locksmith on top of it. 

Typically in an apartment, the boxes are landlord owned and the landlord is responsible for keying and rekeying after a tenant leaves.

If so just rekey the place, take it out of their security deposit, and move on.

If they changed the locks, you need to call a locksmith. 

Saved me from having to get a locksmith out while I was 6 hours away.Really all you are left with after these tools is guest communication and any maintenance.

One of the things they do, when managing a property, is rekey the home so they and the tenants are the only ones who have keys.

One unit turnover usually costs at least a month’s rent after the property manager charges their inspection, rekeying, turn repairs, and placement fees.