We're pretty flexible like that and will keep security deposits if people take the piss.
Not if your BTL is in England or Wales. You have a contract with another person and both parties have to keep to the Housing Acts and comply with the new proposed Act that is going through.
The law changed to stop some people helping themselves to a tenant’s money. From what I remember, that law change was campaigned for by charities like The CAB, Shelter etc
Before that addition to the Housing laws that ended this practice, we used to advise tenants to take out insurance (that only cost about £20 a year) that also provided a legal team of their choosing to take a landlord to court. The insurers then claimed their legal and court costs back from the landlord and the tenant got their money back. This system was clogging the courts and some tenants were worried about going to court, but the law change is much better for everyone, except the bad landlords. In some cases the landlord must pay compensation to a tenant if they haven't followed the law or kept up to date with the law changes.
Now, a landlord must pay the deposit back within 10 days. If the tenant and landlord are in dispute, the landlord can only keep this disputed amount and must give the rest of the deposit back to the tenant. The tenant then disputes this deducted amount with the deposit scheme that the landlord chose, but was required to use.
Once a dispute is raised with that deposit scheme, this usually focuses the mind of the landlord or letting agent, because if they have too may disputes ruled against them, then they are in all sorts of problems with the deposit schemes. The deposit scheme is the one who will decide if an amount is allowed to be deducted under the housing laws and if so, how much that can be.
Some councils' now employ staff just to tackle the bad landlords and letting agents in their area and will peruse these through the courts to clean up their area.