I don't consider the 'type' of leaf (debris) to be removed, but per job, how long is it going to take to complete the clean up.
Do a good job in the first place, and no, a return trip should not be included unless you're billing includes that for some reason in the first place.
Most likely, before you ever leave the job site, new leaves will have fallen/been blown in, so how would you ever get ALL the leaves. Unless it's late enough in your area's season for them all to have fallen.
Clients that want early season clean ups will almost certainly need additional work later in the season. If they are regular clients (not just clean up work) the additional clean up can be done by regular mowing. You're just not cutting the grass in many instances, you're mulching leaves, charge for a mow.