Can't I Forego Something That's Owed to Me?

Justice has to do with owed to someone. But can't I voluntarily forego something that's owed to me? So if I'm selling something, can't I voluntary forego part of the price of it without there being injustice? Well, we're talking about something that hasn't happened yet. No one owes me... If I'mselling something before someone buys it, no one owes me anything. They would owe me such and such amount if they were to buy it. But could I not voluntarily sell it at a lower price? so can I try to take a stab at that?