Trickier question:
Fees?
How much should a contact take when buying for you, selling for you, setting up meets, and so on?
Should loyalty be a factor?
Buying and selling are covered by the core rulebook:
If the contact hasn’t done a lot of business with you, he might ask for a finder’s fee. That’s not how contacts make their money on reselling, though.
So generally, there's no fee when contacts buy for you.
You can always go to a contact such as a fixer or relevant specialist to fence a hot item for you. He or she will happily take your item and offer you five percent of the item’s value times your Loyalty Rating with the contact. You might be able to get more selling it yourself, but your contact will take it off your hands, no questions asked.
So you get [Loyalty x 5%] when fencing (which makes C1L6 contacts both interesting and cheesy).
Finally, fees for obtaining information and getting you into contact with Mission-appropiate NPCs is typically covered by each individual Mission.
