well I've never had him do that dog one or the daggersw one so my maths must be kinda right, he only ever does wakizashi and zanmoto(which I might add I found out means Demon Edge) and I'm only paying him 2500gil mind you I have tried that one before where you give him money that would leave you with a nice round number and I get wakizashi I've not tried the other way but I will, but really its all down to chance you just higher your chance by having good numbers in the other area!!!!
TSA