1. Ideally you should have added the deposit amount held with the AOP, to the sale price and taken that from your buyer
2. going to court is not advisable as the expenses will be greater than the deposit amount
3. for now have a legal notice issued to your buyer with a copy marked to the AOP
4. have you handed all the original title documents to the buyer? if not then you can retain them until he pays up. You can exercise a lien on the title deed for your unpaid dues