Hey Styg,
I have found a bug regarding selling items to merchants for credits (presumably charons, too.) If you move an item into the trade screen and match it with a stack of credits that are worth far less than the item (the bar indicating parity is at the far right) you can continue to add other credit stacks of all magnitudes to the trade. I successfully traded one gasoline drum to Pasqual for 500+ credits (all he had) and an almost broken 5mm Hawker for virtually the same to Lucas. I haven't tested this with other merchants but I assume that the bug affects all of them. Oh, and after you have added the first stack of credits, you have to double-click the other credit stacks. If you drag them, the game responds properly.
Edit:
It works with trading credits, too. Ezra decided my 10 SGS credits were worth 500 of his :smug: