Dwarfs appreciate quality crafts, though trying to pass human craft off as dwarfwork is a way to earn a speedy death, even if you claim it belongs to a rival clan.
I guess Superior Quality would be enough that even they'd recognize it as a respectable gift?
Huh, I realize Dwarfs like Gold, I wonder if a hand-crafted golden arm-ring would be considered a princely greeting gift. We do have some gold lying around after all, and picking up the Jewelry-Trick shouldn't be that hard if we focus on it.
Good beer probably wouldn't hurt either. I don't think they can grow hops.