It isnt as though they were upset that their divorce attorney couldnt answer complex questions about patent law. Free weights should not be considered a niche for a personal trainer in a gym. Even just walking around a gym should show you that primarily you have 3 types of equipment, cardio, weight machines, and free weights, so it isnt as though there is simply too much to learn and understand for somebody whose job it is to be knowledgeable.

The issue with many personal trainers (and people you discuss fitness with in general) is that, for the most part, if your diet is good, doing pretty much anything in the gym will get you results. Many trainers have desirable figures and they know it and they constantly have people asking them for advice in their private lives and are paid to give it at their jobs. This causes many to simply assume that what they did is the "correct" way to workout when the truth is that had they dont most any routine with that devotion for many years, they would have gotten similar results.

This is much more similar to investing in the sense that the experts often give worse recommendations than you could find yourself with a few hours research. Im sorry this is too anecdotal for you, but if you walk into most gyms, talk to most people who have a clue about training, etc, then this is what you hear; people simply arent properly educated on personal fitness even when that is their job

> This causes many to simply assume that what they did is the "correct" way to workout when the truth is that had they dont most any routine with that devotion for many years, they would have gotten similar results.

This. A great example of this is Tim Ferris and The 4 Hour Body. That guy basically says "well, here is what I did, and here's what I look like now. Do exactly as I say and you will too." His "research" has a sample size of 1, yet he claims that his method will work for anyone in the world, from a skinny teenager to his overweight mother. True, it will work for some, further muddying the waters.

This is one anecdote of many.

The thing is, if you work in a gym daily, I'd expect you to have intermediate knowledge of a lot of things: cycling, running, rowing, free weights, warm up exercises, safe stretching techniques, nutrition. The ability to perform assessments of form, fitness, give advice about contra-indicated exercises based on disclosed medical histories, and more.

It's when I see people completely incorrectly adjust their gym bikes, start stretching before they touch any equipment, etc. because their "trainer" told them. When I personally get "corrected" on my "bad" form by a gym trainer (at the time I was attending twice weekly sessions with a qualified amateur lifting trainer instructor), telling me to do the exact opposite of what I was taught. When I see trainers get on the rowing machine and demonstrate poor technique that could lead to repetitive strain back injuries... the list goes on, and it's depressing.

The danger for me was thinking that I knew more than the professional did. Yes, you can be more knowledgeable than the trainer, but would you expect them to know more about, say Ruby, than you do if they dabble in it in addition to their full time job? Seems to me like you can (and probably should) always find a professional who knows her trade better than you do. Otherwise, yes it's a waste of your money, time, and health.

I would absolutely expect to find people in other fields who know specific areas of my field better than me. This is the story of every single person "in computers" since the origin of the career, everyone who dabbles desperate to show that they know some specific better than you.