I think there is a bug with the bribe system. Bods are supposed to increment one level. (I.E. a 10 to a 15, 15 to 20, 20 to better material). However, for footwear (shoes, sandals, boots, thighboots) the 15's skip 20's and go straight to better materials (leather to spined, etc). They aren't supposed to skip 20's I'm pretty sure. No other BOD behaves that way.