Helicopter pickups usually work for me, thought I've a had a few where the helicopter just hovers way up in the air and never lands.
I called for a backup chopper once, and it just hovered near the enemies for a minute and flew away without doing anything.
I called mercenaries on a player for $7500 and as far as I know nothing ever happened.
They shouldn't be paid unless they do their job.
Yeah, the heli pickup is tricky sometimes because if there's anything on the ground, they won't land. I once had to push boxes out of the way. lol
I never use them for a pickup, though. I shoot the pilot and take their heli. I'm a better pilot anyway. Why? Because I would LAND ON f*ckING BOXES!!!!!!!