Yep, same thing happened to me, and I think its a growing trend that some unscrupulous landlords have cottoned on to.
In our case the tenant was happy and paid, the landlord then said it hasnt been cleaned properly and was witholding the deposit. I get a phone call from the tenenat saying that she is now 'unhappy' with the clean and demanded a refund.
I explained that I would visit to see what the problem was, and will even re-clean if rquired. She said no, and that the landlord was going to 'get his own cleaning company that he uses' in to do it properly. I said well what I'll do then is come and see 'this other company' and if they can get it cleaner then I would refund their money.
She said no, and if she didnt get a refund she would report me to trading standards. Well that was the end of that conversation, and left her to it. I think I was being more than fair.
So, yes this is something for CC's to look out for with these types of landlords about - I even doubt whether this landlord even had a cleaning company that he uses.
Mark