The Sneak Thieves
Please sir, may I join your corporation? May I have access to all your shiny things? May I bundle every last one of them into my friends' freighter and dissapear?
Weigh up how well you know people against what you could lose if you turned out to be wrong. People have wheedled their way into confidences and stolen everything from ammo to carriers. Restrict access to hangars to new members, or keep things in your personal hangar if you aren't sure about a director.
In Eve they would be the gate gankers. Usually found watching the gates into low security space occasionally they will hang around in high security space in cheap but powerful ships waiting to explode that faction fitted ship you worked so long to get (sacrificing theirs in the process). Remember 'don't fly what you can't afford to lose' applies in hi-sec too.
'Oh please, kind and strong looking person, won't you help me kill these nasty pie-wats for me. Yes, join my fleet. Here, I'll even warp us. Well, whaddya know, someone I happen to be at war with is here. Strange how he just ignored me and went for you. Still, I'm gonna take all your nice stuff, as you're dead anyway'.
Only join fleets with your alliance or people you know REALLY well, or alternatively YOU set up the fleet and retain control over who gets invited. If you are in control and the only other person is in an NPC corp you are safe enough to be helpful.
'Here, look, a can with interesting things left abandoned. I wonder what's in it? A little ore. Well, there's no-one around so I might as well take it. Wait, where did that ship come from? Why can't I warp? I wasn't really stealing, Concord, help! They said I could have it and everything!'
If it's yellow, it's not yours. They lie in wait cloaked and, when you take it and get flagged for thievery, invite their friends to swoop in to kill you. It doesn't matter how many 'free stuff' signs they pasted on it. Don't fall for it.
So there you are, merrily mining away into a can ready to get your hauler to come get it when you have enough when someone appears in a small ship, pops out a can of his own and puts all your precious ore into it. He is flagged as a thief but he's ina combat ship. But he's not firing. So what do you do. Oh the indignity. Well you take it back of course. Oh, except you are now flagged to him as well, and he can shoot you, or invite his friends to. Damn, here I am in a pod again. Who was it told me high sec space was safe, again?
If this happens to you and you're prepared to lose your ship you could invite your corp to give you backup before you take it back, get them to do it, or you could just chalk it up to experience and leave it there. For real security mine into a passworded, anchored can instead, or just into your cargo.
These come in several different varietes; the buy contract that is just a few zeroes too short, the in-station trader who substitutes a cheaper version at the last second, the sell contract that says it is for a Navy Raven but is actually just for a Raven. Remember the rule of the hustle: if it sounds too good to be true, it probably is.