W
Welder
From the perspective of a customer. If they call you, you cannot pickup then have a nice message for them to leave a voice mail.
After that call back everyone even if you are not interested in the job. The obvious ones are turn up on time, invest in some app or software to help you with dealing with admin, quotes, invoicing etc.
Be clear on pricing over the phone if possible, it will save you a wasted journey which you could spend marketing or brushing up on your skills.
Quite clearly JL, judging by your terribly Corbynesque (idealistic) post, you do not deal with the general public on a daily basis.
The public generally oscillate between Jekyll & Hyde and one never knows which face they'll present until they do.
If people were a little less self obsessed then trades could reasonably expected to act differently.