I don’t generally tip the owner of the business, and that goes for freelancers or independent practitioners. Your prices should reflect the amount you think you should be paid, and you should not solicit additional gratuity.
If you want feedback on customer satisfaction, email them a survey the next day.
When you talk to the client, you need to really cement in their mind that there’s no point in talking to anyone else. When you take that call, what does your script look like?