Some buyers may rationalize that he/she is not taking anything, AND, the sellers pay for it. He/she is not harming anybody.
But the simple fact is that there is a certain value taken away when a buyer opens that seal, and plays with the camera, and then, decided he/she doesn't like it and return it for a full refund. That returned item is not new anymore and a certain value was taken away from it. We all know that the seller just have to raise the price a little bit to cover for this lost value. Everyone else ends up paying more for the value that was taken away.
It is just like insurance fraud. When someone cheats, the honest customers pay for it.
If someone want to be sure he/she likes it before buying it, you can always rent one and try it out. Yes, I know. It costs money. Or, when an item is returned, other than product defect (seller would usually replace it), there is a charge for such voluntary return, instead relying on "the system" to pay for it. Yes, I know. It costs money too.
And here is a philosophical question. Does life always offer a guarantee? You bought a house, a car, marrying a spouse, buy a certain stock investment, getting a job, move to a new city. Do all of this give you a trial an return option. Most of them don't. We have to live up to the decision we make. And when we make a bad decision, we are the one who have to pay for it instead of "someone else".
And don't forget, when without a free return option, you may learn to like something you don't really like initially. And that is live.