It would make sense the option to convert food into metal and viceversa. Obviously with a ratio smaller that 1:1.
For example training two same colour heroes together make the master gains 180 points (first starred training heroes) while mixing colours it gains just 150 points which means loosing 20% of benefit.
So far a ratio of 4:5 or 3:4 would be sane to trade resources. Moreover having a ratio of one gem per 1.000 resources traded with a ratio of 1:1 is fair enough. Adding some randomness that would chose the ratio of current trading could be nice as well (e.g. between 1:2 and 9:10 interval, which would grant about 30/33% of loss on average).
In this scenario the trader could be bribed in gems to increase the ratio by a step from the current and the trading exchange my vary each hour.
How to make make varing the exchange ratio along the time? Four ways:
- random among 5:10 … 9:10 which are five steps
- by a percentage of converting calculated in the previous hour trading accepted by gamers with a logic of selling / buying. Much food gamers are selling for metal higher the prices the metal increase. And viceversa + trader commission (which could be a combination of fix + variable on volume traded).
- like in the previous case but the ratio decrease as much transaction gamers took. In such a way gamers are discouraged to trade among resources to gain time.
- A combination of all of these. In which the the fixed pay-for-transaction fee is calculated by point 3 and the variable part by point 4 plus a random part on the total related to the volatility of the prices which is more or less as a real trading market would work.
A lot of people want make trading? Traders are getting expensive (as long as they could not increase in number and could not manage easily a lot more of transaction, but we assume that kind of complications are useless in the business logic of this game). A lot of food is traded for metal, the metal price rise. A lot of transactions took places between the two? The volatility decreases (on average) compensating the increase of fixed fee but in the case that the volatility increases the increase of trading disavantage would prevent it increase more and more.
Finally, I suggest to implement this trading feature in a simpler way and monitoring the trading. Then advanced the trading model, just in case. May I help you in this development?
Between the food and metal counter a button to trade the two would be a easy to catch GUI.
I hope this helps.