I've never had to choose whether or not to give cargo to a "pirate".
Each and every time that it has happened to me (with one exception, which still ended badly for me), the scenario was the same. I was interdicted, and a moment later, blown out of the sky.
Was I carrying cargo? Didn't matter (in fact, more times than not, I wasn't).
Was I asked about any cargo? Nope.
Was I asked to "drop my shields"? Nope.
Was I trying to run? Nope (as I said, the guns started "a-blazin" on me right after the interdiction....didn't even have time to throttle up).
So, taking into account my personal experiences during my travels in Open Mode, would I give my cargo to a player "pirate"?
Not anymore (if I was ever asked that is). Why bother? The pirating is not for the loot anyway, but for the act of making another submit to a more powerful force, sort of like Hobbs "Leviathan". They're probably going to shoot you down anyway, so why bother complying. When you get interdicted, and you know you're outmatched (which is usually the case), just sit there mute and let them fire away. Sure, you get the rebuy screen, but you probably were going to get that anyway. The "pirate" can have the cargo (if there was any) and a giggle (but a fruitless one), and you can feel good that you were able to brighten someone's day.