From a role play perspective I don't see how this is any different than buying Hoard off a biped. Or having a biped "slave" as a mule. RP-wise, think of this as an excuse to stretch the wings of your imagination and come up with an inventive reason why your Lunus would *want* to buy food from a biped (or demand tribute in exchange for some worthless copper pieces... stupid bipeds! So suggestible).