There's no blurb in the BBB on how to use palming for pickpocketing, so I figured I'd ask:

Is it treated as an opposed test, i.e. the pickpocketer's Palming+Agility vs. the character's Perception+Intuition? Does the victim get a bonus depending on the size of the item being lifted? Does the pickpocket first make a success test to see if he actually lifted anything, and then the mark makes the perception test? What might a pickpocket take from a runner, i.e. commlink, gun, what? And any other questions/points that I might not have thought of.

Perception modifiers, some applicable to palming, are listed on p.117. One of the mentioned factors is "Object/sound stands out in some way", which I would use for a larger object (GM's discretion, always).

I would go out on a limb and suggest the concealability modifiers would apply to the defender's perception test. But the level of 'protection' offered by the defender's clothing should also apply as penalties to to the attacker. E.G.:

On belt or sticking out of pocket: 0
In pocket or under something on a table: -1
In pocket and under jacket, or buried under that stack of NERPS weekly: -2
In buttoned pocket under jacket, or under Rolf The Irritable Troll's foot: -3 to -4.
Snapped to lanyard and under flak jacket, or "Bubba the Barghest's Chewtow he's currently resting his head on: -6.

...Palming also works for concealing items on your person as well.

At the time when palming occurs you would roll the standard Perception roll, modified according to circumstances and item.

If they don't notice then, wait until the next time they try to use the credsticks -- and then let them know they're no longer there.

Edit:

Some gaming styles would make this a secret Perception roll by the GM: one for each player, of course. Others have players make four or five Perception rolls at the beginning of each session, that can be called upon in order for something like this. Yet others have regular random Perception rolls interspersed with the significant ones, to raise both the red herring and paranoia level.

The reasoning is that just by calling for a Perception roll only when a Perception roll is strictly needed, you let your players know something is up.