What makes a good ‘service delivery’ is the user experience – was it good, and did the user get or achieve out of it, what they wanted (ie their goal)?
You don’t have to over think this one – look at your User Journey in providing your service to your client(s) – whether you want to elicit feedback from there via an interview, workshop or survey, or anecdotally from what you know want learn from your interactions with your client, you probably have a good idea what that service looks like.
If you are working in a team, either your own, your own consultancy, or working with the client solo, and you want to improve your service delivery and get more consistency and standardization, documenting your service delivery User Journey, and Processes is the first place to start, just like we/you run transformations – the place to start any transformation (as agreeing the Vision, Strategies, Objectives and Measures) is to understand the current state, to establish the baseline, and build (and/or change) from there.