Est-ce quelqu'un qui vous rendre un service ?
C'est quelqu'un qui vous rendre un service ?
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Both work fine as questions but I'd like to point out that it is not because you are using C'est the same way as Est-ce. It's just the way you phrase it I'm objecting to, for grammar's sake.
You can ask a question:
Just by adding a question mark to the affirmative sentence (and when speaking the intonation differs):
C'est quelqu'un qui vous prête un service ?
By having the subject before the verb:
Est-ce quelqu'un qui vous prête un service ?
(ce stands for c', no elision possible here)
Another question could have been:
Prêter un service is not very clear and that's probably not what you mean. You might mean rendre service (do a favour/lend a hand) or proposer/fournir un service (provide a service).
Edit after OP's comment: