1. There is nothing wrong with pirating in a transport, it ain't the most effective way of doing it, but hey, it's fun.
2. As for selling the goods, in Ivan's case he'll usually only pirate things he can sell himself, or he taxes. Goods we pirate are... Gold, engine components, polymers which can be sold at tripoli, or RP stuff like food pharma etc.
3. If they're goods that are valuable (VIP) but we can't sell ourselves, since OPG can't dock on Kurile, we send in an OTC, our smuggling branch, who are quasi-legal kinda like our personal junkers. They drop by, get the goods, take em to their destination.
4. A flipside to this is, a gunboat pirates a trader, demands he drops half cargo, then an OTC vessel drops by and tractors the good. Combining gunboat firepower and transport cargo space:)