To put it a more geeky way, pretend you're building an API. Would you want your two disparate systems (your services, and the client) to "know" about each other's internals? Of course not. It's no different for business interfacing. All the client wants to know when it inputs Money into You is

1) What are the deliverables?

2) What is the value?

So that's all you should be concerned with "exposing" to their side of the API.