Radioactive tagging means you're outed as a thief the moment you try and sell your loot.
All interplanetary cargo is tagged with an isotope so it can be tracked from planet to planet. This way they can track cargo tainted with Europa-flu, and any stolen goods.
"Radio-readers" are ubiquitous at retail markets across the solar system. It's been enshrined into law that any transaction should be verified by radio-readers.
Even if pirates make off with the cargo, it's been taskedtagged with the victim's ship ID. The moment they try to fence it back into the legal economy, it'll be caught.
Modern piracy = kidnapping
Modern-day Samolioa is a pirate haven because their government collapsed. The pirates didn't loot the cargo ships, but instead held them hostage and demanded ransoms because it's much easier to carry money than goods. Modern pirates don't want your stuff - they want money!
The space pirates have to drive the ship to their outlaw planet - throwing off exaust, radiation, and distress signals (at least until they figure out how to disable that part).
The solar system isn't that big. As this quiz from NASA shows, it would take about 11 hours for a radio wave to traverse from the sun to the edge of the solar system. Even with only modern-day tech - that means a distress signal would be picked up in hours.
It would take a minute to find the first few hijacked ships, but soon they'd zero in on the "Wild West Moon" the government would either nuke everyone from orbit or blockade it and prevent any ships from coming or going until things are sorterd.