i got a normal Maple Harp, and a Maple Harp+1, I casted Knight's Minne, only difference is 1 Defence more....and people pay/charge outrageous prices for this crap...youd be better off synthisizing this than buying....theyre about 10k on Remora last time i checked v.v
All +1 items are the result of an exceptional synth. For example, if someone tries to make a Harp, they may make a Harp +1. It's almost pure luck, though there are some statistics involved, though it's not really worth getting into. The easiest way to think of it is that it just might happen, but it's uncommon.