Meanwhile, how many sales will you lose from actual paying customers who do not like the four hour return period?
Here's a question for you.
How many people who buy eBooks on Amazon actually know there IS a refund period?
Of them, how many even know how to?
Meanwhile, how many sales will you lose from actual paying customers who do not like the four hour return period? Additionally, you will probably face an increase in one star reviews from people unhappy they cannot return the book because they got busy with the kids or phone calls or whatever and just missed the return window. They didn't like the book, didn't think it matched the description and now can't return it. They are probably going to be motivated to leave a bad review to warn others.
Again, why should Amazon be different to the local bookshop at all? You buy the book, but that's it. You might be able to exchange it for another one, but they keep the money. And unless the book is actually damaged, there is no return policy, just maybe an exchange policy. Why should Amazon be any different for eBooks?
Honestly, I know one star reviews happen in products when the deliverers stuff up, and people are that stupid they can't tell the difference, but...
Why should anyone blame an author or a book for a return policy on the platform?
That isn't rational.
As far as the serial refunders go, the tighter the window to be able to do it, the hard you make it for them to do it.
And granted they might just be side copying and then returning, but that's got to be part of the policy. People who do it more than 3 times a month get the returns facility removed from them.