Here’s a quick take on doing commerce in Zap!
For simple “Take this cargo and deliver it” runs, roll the Cargo Bay power of the ship vs. Difficulty 13 for how far (how many scenes) you have to travel before you deliver the cargo and get 1 Wealth Point payoff. You can use the usual rules for combining powers to boost your roll by narrating how your shticks such as Merchant or Smuggler improve your chances. The presumption is that this is the best deal you can currently find, and that you’ve cleverly arranged it so that you’re not going out of your way to do the delivery; that is, wherever you find yourself after that many scenes of travel is the destination for your current cargo. This kind of commerce is incidental to whatever goals you’re pursuing, and should be relatively risk-free; it’s just background texture that give you extra wealth for bothering to make up some details of your merchant activity.
If you’re hired specifically to take cargo X to place Y, that should be the basis of an adventure, and the GM should make up the details and the payoff in WP. This would be the meat of a campaign like Firefly, where the PCs are trying to scratch a living.
If you want to be more of a wheeler and dealer, and actually accumulate wealth, then you would buy and sell commodities. You decide how valuable a cargo you want to take on (expressed in terms of Power Level), and the between you and the GM you make up the details of exactly what might be available at your location. You then pick the power you want to use to acquire it, such as Cargo Bay, Smuggler’s Hidey-hole, Wealth, and apply any narrative “juice” from combination with other powers and shticks to roll against the cargo’s PL roll; if you meet or beat the roll, you get the opportunity to purchase it at the value the cargo rolled. If that’s acceptable to you, you take it on and make a note of the purchase price; the power you used is now committed until you sell the cargo somewhere. Subsequently, wherever you go you can try to negotiate a deal to sell it. Roll the cargo’s PL combined with any narrative juice vs. the Wealth power of the location (depending on the scope of the campaign, this could be a whole planet, a settlement, or even an individual); if the cargo wins, they want to buy it and their offer is whatever they rolled. If that’s acceptable, they get the cargo and you get a profit (or loss, if you’re desperate) in WP of the selling price vs. the purchase price.
The upshot of all this is that you have considerable leeway in how you trade, and pretty large scope for using your powers and shticks creatively to make trading more interesting and improve your profits, while keeping the amount of book-keeping low (no tracking how much space cargo takes up, what your exact current wealth is and if you can afford to purchase the cargo, what prices various planets have offered in the past, etc.).
- Valuable cargoes are harder to acquire, but have a bigger margin for profit; cheap cargoes are easier to get, but have smaller profit margins.
- Poorer buyers are more likely to want what you have, but usually will offer less for it; richer buyers are pickier, but more likely to pay more.
- There’s an “opportunity cost” to keeping goods until you get the best possible trade.
- Gains from trade can be much more than just getting paid for delivery, but it’s possible to lose wealth if you’re unlucky or trade poorly.