Out of curiosity,
have you used third-party property inventory services
before your tenants moved in??
Problems like that one are apart of "fear wear and tear".
I have recently started working with an
small inventory company, where I had to take a number of courses and test and etc. bla, bla.
My point is that
mould is maybe among top 5 reasons for Landlord-tenant issues and clerks are supposed to find stuff like that, so people do not end up in a situation like the one you're in..
PS: Bleach
does work. Tested!
