what is to stop a previous tenant from getting keys cut and returning to a house after it is rented again especially if they leave on a bad note with landlord, should locks be changed?
For a rented property perhaps you could get one of those combination locks to supplement the main ones (e.g. 5 lever mortice deadlock and "Yale" type lock) and change the combination each time the place is rented to new tenants rather than changing all the locks?
Most new houses now are fitted with 3/5 place locking mechanisms, they lock the door both at top bottom and middle, all working from the simple key
The changing of the barrel where the key goes is usually very easy to change
It takes about 10 mins and a replacement barrel costs about €25-35
You can hold onto the old barrell and put it back in in a few years or move the barrells around different houses, if you own more than one and they are compatible
I change the locks everytime a tenant changes, just out of caution for the new tenants