So I just bought the F-150 of jet skis, and am now short on Charons. How do you make some serious money? How much do jetskis generally sell for?
If you're planning to earn charons by hijacking jet skis, I've got some bad news for you: Ray won't buy junk skis or faction/military skis, which seem to be pretty much all of the skis you can steal. If there are any quality skis around to steal, I have yet to spot one, although I haven't explored anywhere near the entire Black Sea yet. As far as I can tell, the option to sell exists solely to get rid of quality skis you've already purchased.
Yeah, it's like that. Imagine Styg flipping you the bird from his lair in Serbia, and you've got the right idea.
As for how to make money, you're in luck, because you're currently conversing with the grand high shekelmeister, the merriest meandering merchant, and the most potent shalomancer of Underrail.
For starters and to state the obvious, loot (or more properly, completed pieces of gear) is your main source of income, and the Mercantile skill will boost your profits immensely. Mercantile will aid you in less straightforward ways than increasing your per-sale profits and lowering your per-purchase costs, however. With a high Mercantile (85+), you can purchase the components for gear of all kinds (guns, armor, and especially electronics) from merchants, craft them into finished products, and then sell those products back for a profit. This is important for two main reasons: electronic loot is always in short supply; and some items are worth so much individually (20k+) that you'll need to barter them for more than just the charons the vendor is carrying, so it's helpful to grab any ammo and good components they're carrying, because the ammo and resultant finished products can be sold on to other merchants. The Power Management feat will greatly increase profits from sales of constructed electronic gear.
Speaking of ammo, it can be helpful to trade excess loot for it whenever possible, because ammo is almost as good as charons. Many merchants accept it in unlimited quantities, especially general goods merchants, who are otherwise difficult to extract charons from, since they only buy bits and pieces. Obviously you take a loss here by buying and then reselling ammo, but a high Mercantile helps, and the ultimate goal is to pile up pure charons.
Of special note are crossbows. Few merchants purchase them, and most who do don't have jack shit to trade for them. Lucas in the SGS armory is a major exception, because he buys crossbows and sells ammo. Always trade crossbows with him for ammo.
Furthermore, and very importantly, always repair loot before selling it in order to maximize its value. To accumulate a lot of repair kits, recycle cheap loot (basic leather armor, daggers, sledgehammers, leather from rathounds and such) and turn that into repair kits. Also, trade with merchants for daggers and balaclavas with good cost:durability ratios, recycle those, and turn them into repair kits, too. Finally, the repair kits themselves can be sold to a few merchants, so take about fifteen advanced repair kits with you on merchant runs.
In order to get lots of electronic repair kits as cheaply as possible, ideally buy the components for basic psionic headbands, craft them, and then recycle them into repair kits. If necessary, buy complete basic psionic headbands and turn them into kits. I say "basic" because the ones with mods are better off being sold directly than deconstructed, because mods greatly increase the value but don't increase durability (i.e., how many electronics scrap you'll get from recycling them).
As you can see, you'll need at least decent crafting skills and a good Mercantile skill to truly get the most out of all this. That's just how it is.