3 issues like that out of 450 orders? I wish I had your problems…
First issue - a difficult buyer who didnt know what they were doing. Once someone starts being as unreasonable as that, just send them a “go away” (in nice words) message and after that, then block them.
The second one was your fault. You delivered before the review was published so how could you expect the buyer to be happy? (I presume this was back when review gigs were allowed?). As you said, the review was published 10 days later - that’s when you should have delivered the order, when it was actually done. Amazon delaying its publication is nothing to do with the buyer - you need to manage those things if you rely on a third party.
The third one. This kind of complaint from some buyers is a pretty standard thing. If you are sure the work is good then you need to explain and prove your position to the buyer. Running to CS every time you get an issue like that is a waste of your and their time.
CS are there to look after their buyers and sellers - they are not there to be YOUR customer service rep to your clients - you need to do that yourself. If you cannot deal with such basic customer follow-up issues then perhaps you should consider only working for agencies - the type that can take on all these issues for you and charge you 50-70% for the privilege.
CS can’t tell or decide whether your translation is done well or not - they would need specific staff to cover every single category, language etc. Instead, they state that quality of the deliverable is not a valid reason for cancellation - This empowers you to deal with the client yourself which is what you must do.
Many buyers of translation services do try different methods to test the quality of the translation as they don’t understand the language themselves. Instead of being reactive in your way of dealing with this, why not be proactive instead? When you translate, do you include “translator’s notes” to explain your choice of certain words or phrases? Every text can be translated slightly differently so point out why you chose to say “The tall man sat down” instead of “The tall man took his seat” by adding a comment to the text.
This approach will help to convince a lot of buyers that you actually did the work properly. It won’t help in all situations of course but in those situations just suck it up. As I said in the beginning, 3 issues, one of which was clearly your fault, in 3 years is pretty much the Nirvana of freelancing careers - count yourself lucky!