I see this and similar being said but I disagree so apparently I can't grasp it either.
Having personal experience with a source is not a prerequisite to forming an opinion about them.
Whether the opinion carries weight should be judged on the substance of the opinion rather than merely an experience. The experience could be something trivial like the source responded to a PM about an order, picked up money, etc.
So, just as you would like people without experience to keep their "pie-hole shut" I would like people that had a trivial experience to do the same.