It's also not uncommon for many parents to employ their kids over the table at exactly or above market rate and let the kid develop experience and get paid at the expense of the parent's other employees. This is legal in most cases, but that doesn't mean that every parent would do it—I personally would steer well clear of this kind of arrangement to avoid even the appearance of nepotism.

With either type of arrangement, I think it does tell you something about the parent-child relationship, which in turn does influence how you should take the parent's testimony.