Isn't it also like chairs, beds, pillows, glasses' frames, bras, mice, etc. though? You can often tell when it's terrible but not when it's going to still feel good after the first 8 hours of continuous use

Edit: further down the thread someone (https://news.ycombinator.com/item?id=40492169) mentions saddle trials as a potential option, so I guess that confirms it. A saddle library sounds like a good starting point for selecting which one to trial, though!