Butters and lessers are very hard to tell apart, even some mojaves look like lessers. I don't know the exact reason for butters being more expensive, but I have heard that super lessers are known to have birth defects. I don't know how true this is though. I also don't know if butters have the same problem, but I haven't heard of it with butters so that might play into it.

With the internet you never truly know what's fact and what's rumor. Hopefully someone can clear this up.