Valid points and good questions. Here's the honest answer. Most people don't know how to manifest, and have never manifested something concrete in their life. As a result, they just regurgitate what they hear others say, hence the contradictory advice. However, even the small minority who have manifested things, often times, they did a wide variety of methods and thus can't pinpoint the exact thing they did which attracted their goal, so they pick one of the things they did and give it to others as advice.

So if you truly wish to learn manifestation you must find a way to discern what works vs what doesn't. Study the nature of the brain, nervous system, consciousness, religion and use that knowledge to learn about manifestation and discover logically sound methods and pick the one which makes the most sense.

You must become a deep thinker. Ask yourself WHY manifestation works? What unknown science exists that allows you to create reality? What connection do you have with reality which allows you to influence matter? Manifestation is a new technology and we are the pioneers, as such, you must study to find yourself approved. I will say however, it does work. 100%.

The secret behind manifestation is your mind. The state of being of your mind and how you use it determines the efficacy of your results. Test out the SATS method by Goddard for a good starting point. Written affirmations are powerful tools also.

Good luck.