No..... There are many different roads from A to B

Fat nutritionist... no. Handicapped trainer... yes. Ugly fashion artist... yes.
^his choice...............^ probably an accident........^ born that way.

I think you have to at least have BEEN a good athlete, or at least worked towards a goal. People have physical limitations. Why would a world recorder holder in any given event get coaching from someone else? Shouldn't he/she be coaching him/herself? After all this person is the best in the WORLD at what they do. Usually the trainers or coaches were never too well known or very competitive. You have to know what you're doing. Age, genetics, accidents, physical limitations, etc. can all stop someone from being a "decent" athlete, but that doesn't mean the person doesn't know what he/she is doing.

It's hard to judge that way because you can take it both ways:

Fat nutritionist: Maybe he doesn't care about his body or appearance so he stays fat, likes cookies etc, but that doesn't mean his advice is bad. Or, maybe he thinks he knows stuff and applies that to himself, but he sucks so that's why he's fat.

Handicapped trainer: Maybe he had bad luck and got injured and handicapped and he knows his stuff or maybe he practiced weight training with bad form and that got him handicapped so he will do that to you too.

Ugly fashion artist: Maybe he was born that way but you could also expect him to know enough about fashion to make an ugly person look at least respectable.

So you see, you can always go both ways with it.