This would require registration and/or login prior to the create appointment page.
if not it may require a re-query at the end of the appointment to confirm Client type and service compatibility.

I would like to limit the services available by client type.
example:
If client type = "new" then .....

Limit services to only services with that client type association.

Like:
Service "A” is only valid for new clients.
Service "B" is only for prior clients.
Service "C" is for either new or prior clients

Just a thought,

Jim