Under certain conditions, the market can be pumped exploited with OP trades that will generate infinite resources. Below is one example of the exploit:
One needs to firstly invest 3000 metal to buy some other resources, e.g. food, to really depreciate the metal value and raise the food value. Then you take 500 food to trade back more than 3000 metal - you end with a net profit in metal. Furthermore, the food is still highly valued and you can buy huge quantities of other resources with food, resulting in resources being generated from nowhere.
However, this is not consistently working. I tried to reproduce this but did not get these profitable values like Cube did. After many trades, I was eventually able to generate 10K metal after spending 2000 food and 2500 wood (profit?)
Ideally we make changes to the bartering mechanism to prevent this from happening.