Token amount return

Dear advocate, We have a house, for which one party has agreed for certain amount and paid token advance of 9000(no one signed on any document, payment was made to online transaction). My parents didn't like his behaviour and also changed their mind to sell it off to my sister, who is ready to pay all the amount and get registered on her name. So my parents called that buyer and returned the token amount(9k, online payment) saying that "our daughter has agreed to buy the house, if you buy it then we will be in trouble with her in laws". Now that buyer is making lot of nuisance saying that "you have agreed to sell house to me, but you might have got some good amount with another buyer that's y you are cancelling my deal. I will file a cheating case on you. Will bring stay on your house." My parents are literally worried like anything, please suggest what can be done now. One thing is very clear that everything went on verbal, not on any document. What worst thing may happen if he files a cheating case?? First of all will the law agree to file the cheating case without any proofs only but online transaction?? Regards Pavani