Will a customs inspection fleet leave you alone if...say you cruise in with 3 Onslaughts and a Atlas full illegal goods (they overwhelmed)? Or would a destroyer and a couple of frigates acting as customs inspectors be ballsy enough to scan you?
They'll still try to inspect. What will happen then is you'll have the choice of either complying, trying to disengage (in which case they'll harass you -> CR loss, some rep loss for you), or engaging them (in which case they'll run, and this is going to drop the relationship to hostile right away). They've got the weight of the faction's authority behind them, and as long as there aren't open hostilities, there's no reason to run. And if there *are* open hostilities, the question of a customs inspection doesn't come up.
And, if you've got a fleet that heavy, you're not going to be able to sneak in, so punching through isn't really an option. What kind of black market player is going to want to trade with you after making that much noise? That's just asking to be taken down by the authorities.
If the relationship is still at "suspicious" after you were harassed and got away, then you *will* be able to dock legally and trade. Can think of that as sort of muscling the patrol, but not quite to the point where word gets around and it gets really bad. Still, hmm. Let me note this down/think about it a bit.