Charge them for coming to let them in or they can call a locksmith at their own expense.The bigger issue here is the assault and burglaries.

After spending all that money to rekey the house, the tenants want different locks.  

CHANGE THIS TO WHATEVER A LOCKSMITH CHARGES TO OPEN DOORS.

Rekeying locks: -150.00b.

He is asking that I pay for the re-keying of the front door lock.

Next step would have been to call a locksmith...

They did not tell me till after 3 days the door was locked and my recommendation was to call a locksmith-  I was very clear on the keys that were given and that door had none.2nd- The apartment floods- I was not notified till after 24 hours-  It took about 1.5 months from drying to demolition to reinstalling the whole kitchen.  

I have heard some of these scammers will go so far as to tell people they are out of town go ahead and call a locksmith to change the locks.  

Best thing I can suggest is just get out there and network if you start now by the time you are ready you will have a solid understanding of our market and have a team you trust.Also generally on your teams you want to have a Realtor if you want to look at properties on market and have someone research and do paperwork for you, lawyer mainly for if you find of market or owner finance deals, property manager to manage properties if you don't want to manage yourself, and subcontractors (locksmith, electrician, plumber, cleaners, and make ready crew).

There was  a locksmith out there last week.