I don't understand this at all. You can Google and have all the prices right at hand, so comparison shopping by number isn't hard.
You can go to a mattress store and lay on a handful of mattresses and figure out pretty quickly what you like - is the pillow top or foam too soft? Do the coils poke too hard? Too firm? Too heavy for you to move when you need to do the sheets? - You admitted to doing this yourself.
I could never see myself buying a mattress from a company like Casper personally. Returning something like a mattress because you don't like it has got to be a level of hassle that I can't even begin to imagine being worth it, vs just making sure you bought one that you're comfortable with in the first place.