I completed two projects of a buyer in one order. After completing the projects I Delivered them to the buyer. The Buyer did not accepted the delivery for two days, He was online many times. After two days he messed up one project with his php knowledge and apologized for messing things up. And now he wants a dispute.
This is going to depend on a few things:
Was your project provably correct, working and as per a) the Brief and b) your portfolio or any expectations given? Provable can be difficult with code as it works for you bot not for them, esp if their server is running PHP 0.00.1a when you always have the latest version.
If you have been silly enough to have 100% customer satisfaction or unlimited revisions on your gig or profile you have no line to draw as they can call on that.
Have you offered to help solve their problem?
You need to have very clear facts, incl evidence that you have done the right things and approach CS, stating that you did the job right and are happy to get the customer working and therefore a cancellation after the client has all the work but has declined solution is not appropriate.