When should you trust an expert?

I was part of an interesting debate with one of the smartest people I know over a call last night, and I thought I'd put the question to you here:

1. Imagine you are an expert in something, say sustainable energy and mobility.
2. Imagine you are talking about it and telling everyone that the future is going to belong to electric cars and buses.
3. Imagine you have a large investment into Tesla, Inc. that you have declared upfront.

There are two ways to think about this:

1. You are misusing your expertise and professional standing to drive the price of stocks you own up by recommending to everyone that the future belongs to the very kind of commercial enterprise you own equity in. You are a horrible person and perhaps are breaking some kind of law.
2. You are putting your money where your mouth is. If you truly believe your research and expertise and are willing to bet your own money on your conclusions, you are an honest person and your integrity (or faith in your expert conclusions) cannot be doubted.

The exact example we were using was Scott Galloway, Professor of Marketing at NYU Stern School of Business where he teaches Brand Strategy and Digital Marketing to second-year MBA students, who (as a teacher and economist, thereby being an expert on both teaching and money) has gone on record to say big brand educational institutes (like ivy league universities) are now going towards obsolescence and that they need to get with the program if they have to survive. He also offers his own services as a teacher for a far lower price in an online sprint than it would cost someone to attend his offline classes at NYU Stern.

The question being debated was:

1. Is he bad-mouthing offline university education to sell his online classes and thus may not be trusted, thereby misusing his expertise and reputation?
2. Is he not only explaining why offline universities with exorbitant fees are on their way out, but he is also literally betting his money and reputation on it, and thus being the best kind of expert?
3. What do you think? Is one of the explanations more reasonable? Or is it just tomato-tomato? How can you tell?

(Note: The point under discussion isn't whether he is right or wrong in his prediction, but whether his expertise may be trusted or does he have a hidden agenda).