The short answer to this question is YES! Clean the property.
The long answer is: There is a LEGAL and MORAL answer to this question.
We’ll give you the LEGAL ANSWER first: (we are, after all, a LAW firm)
If, during a pre-settlement inspection, the house is found to be in poorer condition than when the buyer viewed it, the buyer could quite possibly make a claim against the seller.
CLAIMS = WASTED $$$$
We don’t like wasting money, so we advise all our clients to clean their homes before moving. (Or rather, once they have moved out).
Morally, you should clean your former home because it’s the right thing to do. And because Karma is NASTY.