Hi Jill,
You should be able to do this with a workflow. The workflow should be on the Posted Field entity. What you would need to do is create some if statements:
If Posted Field: Field equals Service
If Posted Field: Contact contains data
If Posted Field: Value equals Service A
Marking Lists > Update Marketing Lists (Add the contact to the correct Static Marketing List)
If Posted Field: value equals Service B
Marking Lists > Update Marketing Lists (Add the contact to the correct Static Marketing List)
If Posted Field: Posted Form: Lead contains data
If Posted Field: Value equals Service A
Marking Lists > Update Marketing Lists (Add the contact to the correct Static Marketing List)
If Posted Field: value equals Service B
Marking Lists > Update Marketing Lists (Add the contact to the correct Static Marketing List)
I hope that helps!