When smuggling, the chance that they'll find "suspicious cargo" in your holds is based on the amount of goods you have relative to your max capacity, iirc. But they'll never seize dropped goods as long as they're legal. So, right before a search, you'll want to drop all of it, and pick it up again right after.
So, in my experience this has been an almost risk-free way of smuggling huge quantities of goods. Come in with the transponder on and a couple Mules(P) in your fleet. Buy whatever the hell you want. Right before they search you, dump everything except for the illegal goods. Since you have a low quantity of goods relative to your max cargo capacity (just a few drugs/illegal things), they won't find the quantity suspicious and dock rep points. Since you have shielded cargo holds, they won't find your handful of drugs. Once you pass inspection, you can pick everything up and be on your way. Since you can drop it the instant before the inspection, there's virtually no chance of pirates/scavengers picking it up.
The problem is how easy it is to bypass the suspicious cargo quantity mechanism, which is supposed to make smuggling even legal goods challenging.
There's another smuggling tactic exploiting the contraband search cooldown, useful for when you need to smuggle 2000 drugs at once. First, do any random black market trading in order to raise your suspicion. Buy a bunch of Ores and sell it right back, it doesn't matter. Let the fast picket search you, and then, because of the cooldown, you can stuff your fleet full of drugs and waltz right past them on the way out.
These two exploits in combination seem to make smuggling virtually risk-free, even with a giant fleet. It makes going dark and sneaking past patrols absolutely unnecessary unless you're trying to access a hostile market.
I'd suggest that patrols start seizing even legal goods, if they've noticed you've dropped them right before a search. And maybe additional black market activity should reset the cooldown on contraband searches.