In the past tenants have been charged for installing locks on bedroom doors without asking for permission from the landlord – these then have to be removed by a contractor and then repairs/redecoration works are needed to the door.
Some tenants have covered fire alarms in the past, which is a serious contravention of the Tenancy Agreement, please do not do this!
Some tenants have also been caught smoking or having/using drugs inside the house. Again, this contravenes your Tenancy Agreement and you will be fined if found to be doing this during your Tenancy Agreement.
Lastly, some tenants have reported issues such as the shower leaking through the ceiling. When investigated, the reason for the leak was due to the drain being blocked with hair or razor covers etc. – if the reason for the issue/leak is due to your living style then you will be liable for the associated repairs charges; if, for example, the leak was due to a pipe that had burst or a part of the shower was faulty then this would not be chargeable, this is something that the landlord would fix and pay for.