There are very few facts, so I will make up a story which I think fits the available facts very well.
1 Young Ukrainian woman arrives in Phuket for a 1 year stay.
2 She finds a suitable apartment and pays a Bt 32,000 deposit and Bt 32,000 monthly rent in advance.
3 She stays for a year, keeps the place well and passes all routine inspections, and pays her rent on time.
4 Her year is up and she is planning her move to somewhere other than Thailand.
5 She lets this be known casually to the landlady/agent, e.g. as the reason she is not extending the lease.
6 She asks for her deposit back, but the landlady/agent make it clear that is not going to happen.
7 She feels very annoyed and "swindled", and has no time for legal recourse.
8 She knows she is losing her money, but doesn't want the landlady/agent to pocket it.
9 The deposit was to cover any damage that needed to be repaired when she left, so she does some damage.
10 She feels partially redressed, and the "damage", a mattress, some curtains and pillows, a coat of paint and some cleaning up, will not leave a lot of change out of Bt 32,000.
11 The landlady/agent show themselves up as swindlers by suggesting the damage is Bt 350,000, a multiplication of at least 10.
I would say to the landlady/agent som nam na. Try teating people the way you would like to be treated.