I am an avid outdoorsman, cycling, walking, hiking. I live in a large city in the Midwest with a lot of pokestops. Would anyone be interested in paying me some FG to keep their pokemon bag full? All farmed by hand or with a gotcha..

Pm me or post in here

It's illegal trade.

I have paid for leveling services in other games. Any reason why it is illegal?

When you log in with their account, you can see all their data sync to their account.

Unless they are logging in with PTC or a dummy facebook account.

may be intereseted if legal ofc

They already said services is illegal after someone performed a service and didn't get paid then bought the situation to Scammer Accusation. See https://forums.d2jsp.org/topic.php?t=74829794&f=252

If you don't know the person, they can take your Pokemon. If either person doesn't know what they're doing, it carries a ban risk.