Thanks for playing and leaving your feedback!
The 'unlimited' power is a deliberate design feature - it's potential for being over-powered is countered because you can only buy one upgrade per resource per day. You might have full resources one day due to a handy chain of trades, but after a couple of days with a bad table of trades and some family needs hitting you simultaineously, the wolf's back at your door! I wanted to encourage players to study the trades carefull and find chains like these, some complex ones requiring sometimes 4-5 different trades to execute, so I didn't want to put a limit on the max number of trades, just how much they can benefit from one of these exploitative chains of trades. I wanted to make arbitrage simulator which is all about looking for weaknesses like this in the market and exploiting them.
You definitely make a good point though, it does feel like a design flaw when it's really easy and obvious to spot and execute - I'm going to look into running a check on the table of trades each day and prevent chains of just 2 resources from occuring - don't want to make hunting for a bargain too easy!