In my case it was more communication between both parties.
Language barrier. Always a tough situation.
They were so upset by the work I produced they hired a hitman to finish me off. Thankfully they found the hitman in question on Fiverr and I was able to buy a gig extra to neutralise him.
More seriously, my biggest problems come about due to communication problems and some buyers insanely high expectations. the latter doesn’t happen too frequently but after a while you get a kind of sixth sense for people who might be about to start giving you hell and I just cancel the orders in question.