The limit for Frost Dragon Bones is 5k, not 25k. I don't believe they are really traded on Sythe. Last I checked, they were also slowly dropping... hardly a candidate for a traded item on Sythe?
I doubt he is still buying.
The purpose of this thread was that we bought at max and sold to him for med. (this would make us lose quite a lot) But since they seem to crash a little, he'll prolly just buy them low in GE himself