So, here's the idea: a guillotine. The guillotine is a huge market exchange when you code it, but on the outside is just a regular guillotine. Anyone can sell and buy from the guillotine. You can sell your resources and get silver or gold; items like gold bars or gems would yield more gold, for example. You can also buy resources, but only the ones left there before, and in fixed amounts (e.g. someone has sold 500 timber before you, so you can buy 100 timber). And here's the catch: apart from calculating your due cash, it also calculates your chance to survive the trade. Hey, you're trading, you have to face a risk.
When buying, the risk is lower (but it also depends on what you're buying), say, 30-40% lower. Selling, though, means a bigger risk, but you can also get a huge amount of money this way. Plus some skill (trading skill is already taken, so something else) that would work for a nice tag.
The guillotine merchant...sounds so nice...????