St. Marlo did indeed have an unwritten rule—you bid 1 G coin, but this so-called 1 G coin is not as simple for ordinary people. There was a precedent where an obscure fool competed with some mysterious tycoon at auction. As a result, before he even left the Death Desert, he had evaporated from this world. This goes to show that St. Marlo's so-called security protection is only established on the rules it sets. Offending the interests of a big shot means nothing would be effective anymore.
The reason Bella bid 1 G was to show goodwill to TK and even to expect some secret trade effects from this gesture. This much was still understandable. Since it was someone else's affair, Feng Yi chose not to bid.