@Yi-Shin0 No matter how many unreasonable demands you cave in to, the guest can still turn around and leave you a bad review if they want to. And as you well know, the guest's review can still be published even if you fail to submit your own (to the great detriment of the hosting community). So what's the use in acting like a doormat?
You're a very experienced host with absolutely stellar reviews. There's absolutely no reason that you should tolerate this kind of behavior. Put your foot down and command the respect you deserve. Say "no," keep your conversation in the messenger so there's a paper trail, and if guests threaten a bad review, report them for extortion.
Airbnb can mediate in payment disputes if you ask them to, but in these cases the manipulative guests tend to win. They can't really help you much here. You're the boss of your business, and sometimes you have to act like one. If dealing with confrontational types is not your strong suit, I'd suggest either enlisting a co-host who can help you do the dirty work, or leaving off Instant Book and screening guests for communication and reviews.