Once you really know how to get a good result then:
Wear a uniform consisting of good waterproof shoes, long pants, a belt with no buckle, a pull over shirt - I suggest a polo style if you plan to work really high end - sun glasses - non-polarized so you can use the sun to see defects without burning your retinas and a hat. No rings, and if you wear a watch, one that won't scratch the paint if it comes in contact. I have a titanium watch that's smooth and then of course plastic watches.
When you go to work, be "at work." Move with intention and stay focused on the work.
If your customer is watching, explain what you're doing and why. If someone else walks up and starts watching, do the same.
Be polite, look your customers in the eye, have confidence that you can and will do the job and that the money you're asking for is fair - both to your customer and yourself.
If there's something on the car you can't fix - bring it up when the car is done - don't let the customer find it. Tell them what it is, and why you couldn't get it. Don't let them think you just missed something.
When your client says, "You did a great job." or words to that effect, don't say thank you. Say, "I'm glad you like my work. I hope you'll tell people about me." or words to that effect. Don't say thank you, wait till they refer someone then call them and thank them, give them something next time you do their car, a token of your appreciation for the referral.
When I start on someone's car, I empty my right front pocket. Then, if I find some loose change, money, jewelry, etc. I put it in that pocket. When I'm done, I empty that pocket into their hands. Sometimes what I've found in their cars has paid for the detail tens of times. Also, empty the vacuum after every job and check it for valuables. Accidentally taking something isn't functionally different from doing it on purpose.
If you do these things, then your work will be the issue. If your work is good you should be OK, if not, you'll have to find a job.
Robert