Whenever you trade, no matter you do that intentionally or unintentionally, the bug is taking effect and affects how many gold AI may charge/offer you, you're already using exploit.
That's why I ban all sorts of tradings in my games.
Uhm, no. It's probably just the same rounding bug that let you trade 1 horse for 2gpt in civ5, but will only pay 3gpt for 2 horses. Never seemed to affect luxury trading and the like...and if the AI seems to offer you unreasonable deals, just decline.