disputing return of deposit

Tenancy Deposits

OK, so I'm actually asking on behalf of a friend who I believe is being unfairly treated by the agent and / or the landlord at the end of their tenancy.

They left the property prior to the end date which they notified the agent off and enquired regards handover but received no proper or formal response. I was at the property when they left and can vouch that they left it in a fair and reasonable state. The landlord is claiming for cleaning and carpet cleaning although these things hadn't taken place before the tenancy begain. They also are claiming for minor things such as small dent in fridge door, this to me would be fair wear and tear. They had been in the property for 3.5 years and the agents had always complemented on how well they looked after the property at the regular property check. 

Question is how best do they go about disputing the claims made by the landlord?

Appreciate any help even if this does appear to be a poacher turned gamekeeper situation. 

Many thanks in advance