Here is one...
You can buy much at pirates' (open and black) markets, say... a pile of ore here, some fighter wings or broken shuttles there, and maybe a couple plasma cannons or other heavy weapons. Afterwards, take a minor or moderate reputation hit with other factions in the system. Maybe go from cooperative to friendly at worst. Meanwhile, pirates do not mind that you traded with them, even at the Black Market (unless it is at Umbra...).
You get caught smuggling at another faction's black market, (e.g., buying a cruiser or a couple heavy weapons), and reputation gets set at -31 (or minor penalty if already inhospitable), which is a gigantic reputation hit when relations were over 75. You also lose access to that faction's market for a while.
Umbra will investigate smuggling when relations with pirates are already hostile. Big deal. However, the constant smuggling message spam might be punishment enough to discourage smuggling there.
Moral of this story, when you need to smuggle, and pirates have what you want or need, take it from them (in Corvus or Magec). Why risk your reputation with other factions when pirates do not care. Better to take a guaranteed reputation hit that a few battles with bounty fleets can fix, than take the big hit that can be tedious to fix.