I've raised this before and didn't visit the forum to respond to questions. Sorry.
The issue is, we are limited as to when we can "rate" avatars. If you are friends with them, you can rate them any time by 1st) pulling up your friends list and 2nd) opening their profile. The Rate... button is enabled for rating friends. But that's about it.
Now, if someone comes up with Wiz-bang-gadget and you never meet the person, you cannot rate them off their profile. You might even talk with them (IM) but still cannot rate them. They might even add a feature, send you and upgrade, give you a free gift, but still, you cannot rate them off the profile because the Rate... button is disasbled!
Well, that's my gripe. I suppose I can keep my 25 to 75 lindens and forget it, but I think it's a d*** silly restriction.