And I'll found Black Hole Markets: A place where discerning civilizations can set up their colonies free from Galactic surveillance, most likely by connecting a wormhole to someplace that is not actually in the galaxy.
...or since we're talking about catering to slavers, I'm more likely to set up a fleet around a black hole, where I charge ships to fly into, and provide a shiny red button that is guaranteed to bring them back. Nobody has complained that it doesn't work, thus it must work, right?
I have a little respect for those pops: While I wouldn't want to get enslaved by aliens, I think if I did that I'd chose the butterflies over everyone else. Sure, they might hurt people that don't work hard enough, not pay them for their work, and generally be complete assholes, but they're too cute to hold it against them.
I've rarely ever had so much fun as when I played as THE VOID civilisation.
I started off with the pre-FTL mod and a whole bunch of other civilisations, in addition to a mod which allowed you to build/sever hyperlane links and my own mod which just disabled communications spread (meaning, to communicate with someone, you had to border them, and things like the great khan awakening or a crisis did not automatically contact you).
My civilisation were purifiers but there was no one else in the galaxy we could notice, or cared to notice, as we were not keen on exploring & making contact with alien civilisations (indeed the two we did encounter were glassed). We began colonising one nebula which was connected by a wormhole to another one, very quickly severing the hyperlanes with the rest of the galaxy. The other civs were starting to discover FTL and send out explorers, we had little time to remain uncontacted.
We transfer all of our population into the nebula, leaving behind an alien species on our homeworld capital, which we promptly exterminated. This left our capital as a ghost world full of advanced alien infrastructure, and many skeletons of an advanced alien species. For any intrepid archaeologists however, these alien species would be a red herring, as the real creators had already departed.
Hyperlanes, dyson spheres, research stations and fortresses were constructed everywhere throughout our systems. For centuries we amassed our armada in blissful solitude, unaware and uncaring of the changing galaxy around us. No one could warp in, but we could warp out - and we watched with amusement as alien civilisations inherited our old worlds, keeping our infrastructure intact.
The Great Khanates rose and fell thrice, and the purifiers did not care to intervene. The prethoryn scoured the fringe worlds awakening the fallen empires and still, the purifiers did not deign to intervene. A war in heaven broke out as the galaxy was split in two, and the purifiers continued with their peaceful ways. At last the galaxy was divided between a devouring swarm, a gargantuan federation and a few independent warlords, and despite all of their developments, ascensions and singularities - for four hundred years there was a gap in the middle of the map.
Theoretically it should be possible to access this nebula, but no one could scan it. No one could travel into it. Ships gave it a wide berth because it was the ghost nebula, and no one had successfully found a way to navigate it and survive.
Astronomers watched with curiosity at this negative space of the cosmos, wondering at its opacity.
Then the armada arrived, and the cycle continued anew. Whole worlds were scoured and brought to ruin, and in the blink of an eye a galaxy was rendered lifeless. On each barren, lifeless world a sapient species was seeded. In time the cycle would continue again!