Having encountered many different pirate outfits, Ves knew that a trustworthy one practically didn't exist.
The value of the Swordmaidens was that they cared about their reputation for honesty. While this didn't rule out the possibility of betrayal, Ves nonetheless felt much more confident about going into bed with them than with any other gang of pirates.
If Ves let this opportunity to hitch his wagon onto the Swordmaidens go, then he would have to approach some other pirate outfit to do business with the frontier. Without a shared history of fighting and working together, and without approaching a pirate gang that used to be strong but was temporarily down on their luck, he would never obtain such good conditions for a private, under-the-table deal.
Certainly, even though he figured he got off rather cheap, maintaining a relationship with the Swordmaidens could easily cost him billions of credits a year, so the deal he just secured wasn't cheap in absolute terms.
