Almost every serious dispute between a landlord and a departing tenant is about the deposit. Almost all of them are avoidable, and the avoidance happens at the start of the tenancy rather than at the end.
What a deposit is actually for
A deposit covers unpaid rent, unpaid utility bills in the tenant's name, and damage beyond fair wear and tear. That last phrase is where the arguments live.
Fair wear and tear is what happens to a home when someone lives in it carefully: paint dulling, a carpet flattening in the walkway, a tap washer perishing. Damage is what happens when they do not: a cracked basin, a door off its hinges, a wall repainted a colour nobody agreed to.
A deposit is not a redecoration fund. Charging a tenant of three years for a full repaint is charging them for the fact that time passed.
The inventory is the whole game
Take photographs at check-in. Every room, every appliance, the meter readings, and anything already damaged. Have the tenant sign or acknowledge the same set. It takes twenty minutes and it settles every future argument, because both of you are looking at the same evidence.
Without it, a deposit dispute becomes one person's memory against another's, and the person with more to lose usually gives way.