I don't think it is a rarity thing with him. I thought he asked for things based on prices?

It could be which is not good since average prices are never really right these days.

The wizard chooses his items based on price, not just rarity, but weighs heavily toward lower rarities. Sometimes he asks for items that are too much, and you just have to go to the next quest ;).

Everyone please see the above. Locking as this is not a bug!