[sheps]

I'd ask for for proof that the same was done prior to you taking stewardship of the property - if they can't prove the curtains were either new or cleaned immediately prior to you moving in then they cannot rightfully ask that you perform the same on leaving the property - your deposit is taken to ensure you return the property in an equal state to when you moved in - its not for betterment.

I would agree that the extractor should be cleaned.

Otherwise, if the flat is properly cleaned the agent is being a dick by running a finger over door jambs looking for dust. Any self respecting tenant would complete a clean on moving in anyway, regardless of how clean the property appeared.