Due to a few users buying up low rarity items from user shops, and trying to sell them off for tons and tons more in the trades - you can now see the rarity of all items while trading :)
PLEASE make sure to check the rarity, and value of items before you accept a trade (or bid on a pretty item!) from someone who might be trying to trick you :(
! Mercy on the weak of mind who don't bother to check rarity... like myself 8D;
I don't think the staff believes that trade prices are based solely on rarity, this addition just gives people a heads up if they're being asked to pay high prices for low rarity items. There will always be exceptions, like in the case of new highly sought after items for example.