Valid Relationship Types and Service Providers Are Defined On SA Types
You control which services have SA relationships (and which don't) when you set up your SA types. Each SA type can have zero, one or more SA relationship types. Each relationship type, in turn, can have one or more valid service providers.
Fastpath:
Refer to Setting Up SA Relationships For SA Types for the page used to define the service providers and SA relationship types for each SA type.