Any demands that hurt feelings may cause some damage to the property. The most important thing is to get back property safely with minimized damage. Any penalty and deduction should be discussed post-moving. I'd suggestion the following procedure.
1) Ask the tenant if it's ok to put up for rent sign as we speak to buy time to get the property rented faster.
2) Ask the tenant to show the property for potential callers if they agree.
3) Ask the tenant to clean up the property and return the property in good condition.
4) Once they move out, you can discuss the deduction and holding deposit etc.
Normally you don't expect anybody who is leaving the house to pay any more than the last month's rent. However you can do something to hold the deposit. The legitimate reason is that mandatory cleaning fee and vacancy costs.
If you want to go beyond deposit, in case you have multiple month's vacancy, you may try to ask the tenant to pay back. Since the tenant bought a house, they do care about their credit. They may do something good to your property.However they might be tight with cash with their own expenses. The chances are you don't get much back unless you file a lawsuit which may not be worth your effort and time.
Once again, the best strategy is to get the property back in good condition with extra costs on renovation and maintenance. That will be a win-win situation.
