You’re describing something different, which is just paying later. I was objecting to someone proposing reading books and then paying only if they thought it was good. That’s the part that isn’t commerce, because one side is making use of a good and isn’t compensating the other side.

I mean, I also didn't pay for stuff I tried and didn't think was good. (Which reminds me, one day I should actually buy the Warriors series of books since I only read them from a library once...)

I throw money around a lot more now though, I tend to just buy something and try it and only ask for a refund if it's really useless (like was a macOS app called Vivid that ruined video playback; Lunar works much better).

I personally don't think there's anything wrong with not compensating for a good that you can't use. Then you're not using the good without compensation because you're just not using the good. Books are a funny concept because people consider reading it to be using the good.

If I read a book and there's absolutely nothing I can gleam from it and I just hate it, why should I pay for it? Is it the experience of having those words thrown at me that I'm paying for? If yes, did you know some movie theater tickets are refundable if you didn't like the movie after watching it? I think mostly in Canada. Look it up, it's a real thing. Are those theaters implementing commerce incorrectly?

Yes, interesting case. I'd say the difference is that those theatres are agreeing to those terms. With books, I think it's fair to read chapter or two in a bookshop and decide if you want more. But if you read the whole book, you can't then just say "That wasn't great, I won't pay". Nobody agreed to those terms, and you're getting the product of someone's labour and just declining to pay for it.