A trial period would also work, like an hour or so would probably be enough to get a feel for it, and whether you are happy with the quality as presented.
I suppose the somewhat flippant answer to devs. worried about this would be to release better products, don’t rely on users not being able to get their money back.
I’d say more than an hour just because for something like a detailed airliner it’ll take that long the first time just to get yourself familiarized with it and into the air.
But I don’t think that’s flippant to devs for the exact reason you said. I mean the reason people spend so much on add ons for this is that you spend hours and hours and hours flying the add on plane. If an hour or even a day pass is all anyone’s getting out of it well maybe make a better plane. I know I’ll feel ripped off if it’s a 3 flight and done product.
I’m all in on this but I doubt it’ll be put into fruition on the basis of people simply asking for it to done. Perhaps the only way it’ll be implemented is if everyone bands together and stops buying items through the marketplace for a certain period of time, in protest. Its only when it hits them financially will they stop and listen.
I think you can get your money back, it just isn’t easy, as one of the earlier posts mentioned and(i think I’ve read this) there is some kind of limit on how many times microsoft will do this each year on your account.
Edit: the circumstances when they grant a refund may be limited to cases where it doesn’t function for you rather than whether you like it or not though.
Edit edit: Refund Policy
The other way to do it is issue a charge back on your credit card. They really don’t like that though.
Every time I’ve done a charge back I had to get a new card. Hassle.
Apparently MSobo are not as it is almost the end of 2024 and they have not allowed refunds on addons 
The addition of rentals in 2024 will at least mitigate your loss for an addon that doesn’t live up to expectations.
I think the only recourse is using legal means, if we all got together and launched a class action, I believe Microsoft may sit up and take notice and start behaving more reasonably and less like a bully. Meanwhile treat market place with utmost caution. Some addons are really terrible, caveat emptor. 
If vendors and Microsoft allowed a trial period, they will lose a lot of commission on sale, because frankly some of the stuff on there is really bad! 
A successful trial period program would depend on the product being ready for release, not in a Beta state.
+1 to this, and for MSFS 2024 too. I just bought a boat addon and found out that it has a bug where looking through the windows looks very blurry due to DLSS being on, which is basically a requirement for MSFS 2024 to run decently in VR. Makes this addon unusable in first person mode. I’d like my money back!