Foremost, the service of the Asset Store is terrible. There is no any kind of buyer protection at all. If you want to refund your money, you just can forget about that. Yes you may try to send a refund request to asset publisher but in most cases it has no result because the majority of assets available on the Asset Store are not owned by Unity. There are effectively no refunds - any refunds you get are completely up to the asset developer. You need to contact the publisher of the asset directly, only they can authorize a refund. So in most cases you just waste your money, as it is entirely at the publishers' discretion to provide a refund or not.
Uncertainty about refund is the key factor that detains me from purchasing assets, especially the more expensive ones. Yeah, this is a scam! No way to get a refund if the person doesn’t respond. I am pretty sure Unity team has brilliant coders, so why they can’t write a simple refund system? Even Steam has a refund system. There are too many independent developers contributing to the Asset Store - some of them being great, some just average ones, and there are also those on the clearly weak side. They vary greatly in the quality of their skills and support, but no one at Unity seems to care or even try to do something about it since long years. Problem is that money doesn’t grow on trees and home-grown developers are mostly very limited with their funds, no matter how hard they try.
Also take into account that literally thousands of assets on Unity Asset Store are deprecated. The reason for this is that the speed of change in the Unity engine has increased dramatically and instead of having to support one major release every year, Unity are doing significant and breaking changes every quarter and now even making alpha versions of Unity available.
I believe that there is no better solution than to let people grab whatever assets they want for a monthly fee to try and play with them. At the same time, it should be strongly forbidden and highly fined to use those assets in production without paying final full price for them. Unity team should do something about it, and it seems sensible to put their best efforts into this way. Like a group of people or even an automated scan procedure that would be checking on every single new product in the market against proper licensing of its components and request an immediate take-down if anything seemed to be wrong than shamelessly milking people in the way they do for now.
My personal opinion is that the Unity Asset Store is clearly a badly implemented idea that violates several consumer protection laws for now. If you have another opinion or something to add, just write a comment.