What are the benefits and drawbacks of pre-rating users?

I'm working on a website where clients can hire people. After working together, "clients" and "staff" can rate each other from 0-5 stars.

If someone creates a "staff" profile and has never worked with anyone, is it a good idea to start them off with 4/5 stars? Or is it better to leave them in an "unrated" state? Are there any studies on this?

My client wants to pre-rate users, and I've seen this approach on competitors websites. But I am kind of hesitant because it could lead to the rating system to be seen as untrustworthy. On the other hand I'm worried that at launch nobody will have ratings and all users seem untrustworthy.

I appreciate your help!