Then please do not be an arsehole landlord.

It is not the tennant’s responsibility to pay the mortgage on your flat. Nor should they return it to you as new.

What you rent it for is the market rate, which hopefully will cover your mortgage+expenses. It may not, that is your problem, not the tennant’s.

When the tenndnt moves out there will be changes and even damage. Just like your primary property will have changes and damage.

When the tennant highlights an issue, fix it NOW. They are paying you a lot of money and deserve a lot of service.