You’ve got to define a line for yourself and once you’re past that line, you put your foot down. For example, I pretty much never entertain modification requests, unless the buyer can point out where I’ve missed some part of their instructions. That said, if they want something REALLY small, like for me to rephrase a header, I’ll do that. Anything that takes more than, say, two minutes of my time, is out of the question. I put my foot down, let the buyer know that I’m sorry they’re not happy with the piece, but I followed the instructions given to me and fulfilled the expectations of the gig.
In that situation, you have to be ready to take a less than super review. The great thing is that these buyers almost always lie in these reviews (I had one buyer who I went back and forth with for like two days and when he finally left a review, it was /vile./ He said that I’d screamed profanity at him and told him to f*ck off and then he instructed future buyers to contact him before placing an order with me so he could tell them what horrible things I’d done to him. CS could see I obviously hadn’t cursed at him and had been perfectly clear, polite, and reasonable throughout the process). Alternatively, they’ll often threaten you with a bad review before they actually leave it, trying to bully you into giving them free work, which, again, CS doesn’t take kindly to. That means that CS will almost always remove the review.
What I’m basically saying is that you’ve got to figure out at what point you’re going to say, “Sorry, you’ve gotten what you’ve paid for, I can’t spend anymore time on this order.” Maybe not that exactly, but you get the idea. And then stick to it. Maybe bend it a little bit if you get the sense the buyer will leave you a great review if you do just this one revision, but don’t make any real exceptions.
I always feel worse about letting an unreasonable, rude, demanding buyer have their way and win than I do about standing my ground and taking a less than stellar review. But that’s just me. This is how I put a cap on the stress of working on Fiverr, where buyers can pretty much do whatever they want: they don’t get to pull crap with me.
TL;DR: Set boundaries for yourself when it comes to making modifications and dealing with unreasonable/rude people and then STICK TO THEM.