Most recently, there's the time I went to unlock the Guardian FSD Booster. I completed one run of the site, found I didn't have enough Guardian bits and relogged. Upon logging back in, I found myself in an instance with an Anaconda and another DBX. We ended up combining firepower from our little SRVs to take down the Guardian bits. At the end, they got their data from the orb thing and I got the last few materials I needed.
More memorably, there was the time when I'd just finished the basic outfitting for the pirate Corvette I'd decided to buy. I took it out for a spin in my usual haunt and, while I was hunting for the next hauler full of LTDs, I saw a Chieftain or a Challenger, I forget which it was exactly. Having not had the opportunity to pirate another player for quite some time, largely due to not frequenting the popular spots but that's on me I guess, I immediately zeroed in on the unsuspecting pilot. It didn't even matter to me that the Alliance ships weren't your typical trading vessels, I just wanted an interaction. Cue the interdiction and, once we've both dropped into normal space, I notice that he's got less than half hull. It turns out that the other CMDR had been bounty hunting and was on his way back to port when I jumped him. Fortunately, he saw my demands to come to a stop and neither of us had to start shooting. I ran a manifest scan, he explained what he'd been doing and I expressed my (feigned) disgust at his lack of cargo. Since the Corvette had more outfitting space than my previous ship, I had been able to fit a repair limpet controller which I put to good use on the other CMDR's ship. The repairs finished and we parted ways. He seemed pretty relieved that I hadn't blown him up and hopefully the module repairs weren't too costly. (Why the heck can't I repair other people's modules with the limpets?)
Then there was the guy in a Cobra Mk3 that I interdicted during the free Epic giveaway. During the course of our negotiations, he let slip that I was the fourth person to interdict him that day and that the other three had sent him to the rebuy screen. I felt bad and let him go with full cargo. More recently, I like to interdict smaller player ships that I know or suspect are traders. The Type 6s are pretty obvious but occasionally I run into an Asp Explorer or a Cobra that turns out to be a bounty hunter. There's usually this awkward lull in the comms when I figure out they has no cargo and they explain that they're bounty hunting before I let them go. These days I usually let the traders go after exchanging dialogue if they aren't carrying anything really valuable since my usual haul from NPCs is way more lucrative. One guy in a Cobra told me he sank most of his savings into the ship and cargo back when I was still taking player cargo since I hadn't learnt the ropes yet about NPC piracy. I felt bad again, halved my initial demand and then let him bargain me down further. I ended up with five tons of titanium and I followed him in supercruise until I saw him reach the station to make sure nobody else got him since it was an Anarchy controlled system.