Just conjecture at this point as I don't think any non-Amazon employee could know exactly all the details around when Amazon decides to charge a return handling fee, etc. I guess this may be in the fine print somewhere, but I would rather expect the fine print just to say "We can charge you a return handling fee if we want".
My experience is that I tried to return something last year, and Amazon was going to dock 12 dollars of my 14 dollar refund for return shipping if I clicked anything other than "defective". The product wasn't defective so I just decided to keep it, not worth the hassle for a $2 refund.
Did you order from a third-party FBA seller? If you did, they will often tell unsatisfied customers to keep the product and issue a refund anyway, because they'd rather be out one unit than have a return against them.
Of course, this means that customers always choose that option, and FBA sellers get harmful demerits on their account every time that happens. This is such a popular way to hurt FBA sellers that people have a habit of ordering items from competitors just to return them as counterfeit and/or defective, in the hope that doing this a few times will get a competitor removed from the seller pool.