I kind of figured back-alley deals and fences were going to be a staple in the game.
I think the mechanic in GTA IV was pretty good, though it could use some tweaking. Once you call your contact, you set up a time to meet them, rather than them just magically appearing nearby. Take too long or otherwise miss your target window, and they take off before you get there.
I do like the feel of the back-alley, out-of-the trunk deal, but I'd also like to see the chance of cops crusing by, and busting the deal, or some Boostergang that's feeling froggy, thinking they can come up on free warez / gear.
Black Market sellers and Ripperdocs should be a given. I want there to be an elaborate network a Player has to navigate in order to find many of them. 6 degrees of Fixer Separation. Making some of the high-end blackmarket sellers or ripperdocs almost being eastereggs in how hard they are to find.
I also want 'bogus' blackmarket items. That guy who sells you a 9mm silencer for half-price, then once yo install it you realize you got ripped off and it's just threaded pipe.
And that Martial Arts skill chip, not until you install it will you find it is a paralyzing virus and the ripperdoc is just waiting for you to collapse to strip you for spare parts
Definitely need black market dealers
need somewhere to get that really edgy piece of hardware , sell that dirty piece of stolen tech , grab the newest gear not yet released to the public in Night City but its available in Japan etc
I agree they should be difficult to find , you gotta have good awareness/notice Human perception and /or persuasion/fast talk to actually get a good deal
and maybe if your reps high enough they come looking for you
Also, I'd like some awareness ability to see if you're getting ripped off. High Weaponsmith might help you see that the Araskaka SMG that dude in the van is trying to sell has a busted bolt carrier. Or a high Cybertech Skill might help you see that those blackmarket cybereyes are bunk. That'll 'encourage' players to pump those skills up instead of just twinking out all their combat skills.