Same for me. I was not trained by a relative. When I had my firm, we always had trainees, and none of them were ever relatives. We viewed it as a long term commitment to growing the business - and that meant the arrangement had to be beneficial to both parties, or the trainee would simply leave a soon as they got credentials of their own.
It is far easier to make training mutually beneficial in a firm with multiple appraisers, but the fact is most residential appraisers work as sole practitioners. The economics of training in a firm are very different than the economics of training in a one-person company. I do not mean that as any sort of criticism of those who work solo; it is just economic reality.