When the guru’s only product is the secret, the secret is that there’s no other product.

When the entire offer is a hidden method, there is usually nothing standing behind it. People who have actually built something tend to talk about the building, because they find it interesting and because the details were never the scarce part. The ones selling access to a secret depend on you never checking whether the secret produced anything except the sale.

Before you pay for a shortcut, look for what the person made outside of teaching it. Ask what they would still have if nobody bought the course. That question sorts the field quickly.