As far as I know, Itch does not do any automatic refunding. You might have noticed, that there is no button to request a refund. None at all. You need to contact support. That is an email. With text in it, that the customer wrote, explaining what the problem is.
and then later ask for a refund because they changed their minds / no longer need it
That would not be an eliglible refund reason. But in some cases Itch staff might grant it anways. They want customers to be happy.
My assumption is, there are not that many refund requests to begin with and they know pretty well wich ones are frivoulous. My reasoning is, if they were swamped with refund requests, they would have implemented a better system with more automatisms.
Maybe it is different with assets, but I have read literally thousands of game descriptions on Itch. Talking about refunds is not a thing. At least not in the description. And I do not remember anyone advertising their refund policy specifically. Or advertisng the fact that there are no general refunds for buyer's remorse.
If you do not want to change policy significantly, spelling out the obvious might have a detrimental effect. You put the concept of refund in the mind of the buyer.
Typically, when a refund policy is advertised, than for one of two reasons: to protect yourself from people trying to get refunds that you would not grant. And to really advertise how good your shop is, and that you can buy without worry, since it is so easy to refund items.