I don't know if you can do it or not. In PSO2 it will give you a warning if you try to sell a rare item to the shop. I accidentally sold my Mercurius Rod and don't want other people to make the same mistake
It appears that for some people, shop NPCs are more dangerous than Ragol's monsters.
"Sell me your weapon."
"Sell me your weapon!"
"What? I can't stop myself from pressing Enter! Nooo!"