I have experienced this while taking a big project! When I got a custom order which has 2 to 3 days work! I do message client, but he dont answer! So I finished the work with the instructions he gave and I delivered the file! After few hours I got notification of modification requested in which he updated everything which will take another one day for me to work! Later I submitted the updated work! But he wants me to improve something! He was not satisfied! But as a seller , I sold out many service which completely satisfies all the customers! But this buyer is asking for a new update or he wants to cancel the order! If he cancel the order, I will be affected too much! He also has a source files too! And I do another update, I am not sure, he will accept! At this point, what to do? Someone please give me your advice and opinion! I dont want to loose my hard earned money! Someone please give me some advice for how to deal this!
Essentially I just answered this here: What if buyer takes the idea and cancels the order? - Welcome / New User Introductions! - Fiverr Community Forum
Every time you let a bad buyer be a bad buyer, you just encourage them and those like them. Stand firm. So long as you have done what was requested, the work matches your portfolio or other examples sent, you are not responsible for their poor buying skills or outright fibbing.