I'd call a locksmith to remove the lock install another controlkey lock supply the tenant with a new key and bill the tenant for it.

I'd also make sure you have a locksmith lined up to change the locks. 

Regarding the back door you may need to get a lock smith in there to switch out the lock, which should not be very expensive. 

Vendor sponsors are only people he's done business with (insurance, locksmith, appraiser) and they're all very well-regarded by other investors who have used them.The investors who are unhappy sound like they have a right to be, but I don't know the other side of the story.

I sent a locksmith to replace a lockbox on the property because the code I was given to the box doesn't work.

Get a good locksmith or re-key company to help you out with the new locks.

The seller took a picture of the door and called a locksmith to reinforce it, but locksmith didn’t get there before the door was broken and the property was entered illegally.

That's great that it is a quicker process to get squatters out, but if you have squatters in the first place that would be a red flag for me that somebody dropped the ball (bad location, poor management company, bad locksmith etc.)

You're going to want to contact a locksmith to open the door for you and then change the locks as the previous owner may still have the keys to the property.

.=, cost of you time screening applicants and answering all the questions over the phone, cost of preparing return of security deposit and taking new deposit,   cost of a locksmith to chance locks,  all in all  it should be about 2 months work of rent.The tenants have no idea what it takes to transition property to someone new.