I've ordered a total of 10 SKS rifles using my CR license in a batch of 6 and a batch of 4. I've never had the option of "handpick" from the places I've ordered.
I can say that in the batch of 6, there were 2 rifles that were visually much more appealing than the remaining 4. And in the batch of 4, 1 of them was clearly nicer than the others.
So, my conclusion is that if the distributor was grabbing these 2 rifles from these 10, I would have likely gotten the better 2 of them, cosmetically speaking.
For an extra $10, is it worth it? Depends. I would say that if you are ordering $100 rifles, adding 10% for cosmetics (which can be subjective) is NOT worth it. Save the $10 and for every 10 rifles you buy treat yourself to another one on your savings. If it's just for shooting and not for collecting, not worth it. But if you're buying $500 CR guns, then $10 would be a smaller percent of the total, so then it may be worth it.
It may not be worth it if the guns are all "very good condition" but it would also be worth it if the guns range from "good to very good" condition.