The exploit has been introduced with EE Patch 2.7.
“Poseidon: Increased the trade rate bonus from +10% → +15%.”
The trade bonus and Tax Collectors tech together make you rich. All you have to do is:
Buy 100 Food, sell 100 food, buy 100 food, sell 100 food…
And you will have more gold than before.
The process can be accelerated with hotkeys and you can earn a huge amount of gold easily:
Reproduction steps are added in the video’s description.
I hope that patch 2.9 will release soon and will fix all the bugs I reported here.