Donation is quite ridiculous.
It is a marketplace, would you after doing shopping at your local ALDI store, pop back in and give the checkout chick $5.00 ?
If you wish to recognise an author, by giving them extra money buy the product or buy another product of theirs or buy it again.
Donation systems, open up a whole can of “taxation” issues when run thru a “i sell products, you buy them” marketplace.
Further, having a donate link on a page would further security vulnerabilities by having to incorporate every known donation banking system within the marketplace pages.
So not a good idea in my opinion, but a viable alternative is message author direct and ask if they accept donations separately via paypal or other.
Ste