[figgyc]

Perhaps they could limit refunded products to 3 star or below? Really there isn't a good reason to positively review something and take it back, if it was your fault eg if it didn't fit, then you could just not review it.

[takeda]

There are probably multiple ways, but often it's fine by providing the product for free in exchange for a good review.

They can for example provide a coupon that will reduce the price.

[heartbeats]

What if you refund out-of-band?

[frandroid]

That's what usually happens. Amusingly, in the form of Amazon gift cards (so you go out and buy more products for review...)