Unfortunately this happens. Buyers get caught up with the sales pitch and after they win they start doing their due diligence.
Probably seeing your account linked to 2 banned and 1 suspended account didn't do you any favors. Also checking your claim of unique content and finding the exact same articles on websites you sold previously didn't help either. Your feedback score of 0% from two buyers could have caused concern. Or maybe it was your current status of "Verified invalid phone number" that caught their eye. Making false claims of 5,000 unique visitors a month for a long tail that Google says doesn't get searched once a month isn't very believable. If you're going to make a claim of 5,000 a month you better have some damn good keywords that get searched and you better rank for top spots. Deleting two comments from inquiring bidders during the listing most likely caused concern and using an excuse you're linked to a banned account because you forgot your password and didn't pay a Flippa fee is pretty lame. There are ways to retrieve a password.
Not all buyers are complete fools although Flippa has their fair share. I can see why the buyer backed out of the sale. Good luck with your relist for the 3rd time now. I doubt it will go much better that the previous two times.