I drop everything at once, but sometimes it's not possible if there's more than 10, and I'm not sure if other cmdr has large backpack mod. It's better to not drop everything at once,
'cause sometimes visibility is not good, things can sink in the grounds in high G etc. About trust - I did this exchanges about 10 times, with 7 - 8 cmdrs, not sure, and everything was ok. In the end - what have I got to lose? Some data which I don't need? SRV destroyed? I have 4 of them in Krait Phantom. Even if my ship is destroyed - it's 8 M rebuy and I have 40 B from playing Horizons. So, I don't care. If somebody will come to kill me, I will search for revenge later, and it can bring some liveliness and excitement in the game
But what can I get from exchanges? Some friends in the game. That's a big win.