You usually never choose your buyers or cannot know them completely with few chat. I too am doing freelancing on fiverr sonce last 1 year, and have meet this kind of buyers this month only. If you haven’t meet its not you will never meet such buyers. If fiverr allow these kind of cancellation, what is even the logic of customer acceptance, 3 days waiting, 14 days security period. Everything seems waste if they can cancel it after 20-30 and any number of days. Just buyer have to open multiple tickets.