The problem isn't that parents can't tell them apart so they buy the wrong one.
The problem is that parents can't tell them apart so they buy one and then never buy any of the others because they're 100% confident their kid already has the gray and gold dinosaur.
No, the problem is you conveniently left out the rest of the paragraph you quoted, especially the very next sentence:
Mommy comes home and says "Here, Billy. This is the one you wanted right?"
"No, Mom, that's Slag! I already have him, see. I need to get Snarl, the stegosaurus."
"Ok, well we'll go back tomorrow and see if they have the right one. ok?"
It's not as if said parent is not going to try and get their kid the right toy. You make it seem as if people will go and buy only one figure, and the kid be dammed if he already has it, or it's not the right one.
This is why stores have return policies in the first place.
I dunno, if I was the parent, I'd probably be like, 'I'm sorry, I'll get the right one next time." And then next time would just be the next time I got them a toy, which could be whenever. I wouldn't go back to swap.
I would. In fact, I remember a couple times as a kid when I got a toy I already had and my parents took me to the store to exchange it.