I can't imagine buying or selling most high-value items on Amazon: the buying side has already been covered in various places (https://seliger.com/2017/01/09/tools-continued-careful-buy-a...). I've sold cameras and lenses on Craigslist, which can have its own challenges, but never one as expensive as an A7R IV.
When I used to sell bikes/parts on CL, my rule was anything over 200$ I would only do in-person and locally (Besides, any full bikes in that price are probably too expensive to ship.)
And frankly, If it's something you have a hobby doing, you can wind up meeting some people who share your interests. When I sold a Mountain Bike to a guy we wound up meeting in front of a CVS and just shot the shit for a good half hour after the sale.
I spend tens of thousands of dollars on Amazon every year, buying everything from electronics to groceries to paper towels, and have never had any issues that were not resolved to my satisfaction.
