In the Facebook group for Hypernode Media's Planet Mercenary, the question was raised of how to introduce plot hooks. I suggested in the thread that, if you don't feel like pushing plot hooks, or a player wants to try to weigh some offers, they should make a skill check to search for new contracts. Except, what skill is best for it? My primary suggestion was Economics, both because it discusses finding new business contacts, and because it's otherwise an odd skill for most mercenaries to pick up, so it's good to find a use for it. Alternately, Empathy would work, but that seems more like hitting up friends for work than looking for new sources.
Economics does look as if it would be the skill most often used for this, but I doubt it's the only one you can ever use. History might occasionally tell you about an old grudge that someone might pay to have resolved (or made worse), and Research could boost whatever skill you're using.
The creator of the system, Alan Bahr, also weighed in on it (but said he doesn't do Stack Exchange):
If you're getting it from criminals: Negotiate (Black Market), Military: History (Military).
And I'd always allow the Contracts skill.
Naked plot hooks seem pretty source-material appropriate to me. "Your crawler on the job boards has turned up the following opportunities that match your capabilities: a, b, c. If any of these seem appealing you can open negotiations." That's more or less how I do it in the game I'm currently running. If there's any other avenues the players want to pursue in turning things up, that seems like something that would rely on their initiative and creativity.