Asking feedback from the customer after delivering service, is crucial. You can either lose them or can build a permanent relationship with them. So anyhow never lose this chance.
Look at the attached Image.
The first message might look descriptive and to the point. But it lacks cordialness.
The second mail looks bulky but it can be 4 times more beneficial than the first one. You can read those 4 benefits here: https://thehustlingbears.com/letter/strategy-4-more-friends-fewer-customers