I always thought selling a good product is easy.

Creating a good product that is hard.

And selling a bad product is hard so the people with this skill makes a lot of money.

Creating a good product requires lots of interaction with your target customers. You can call the "sales" in the beginning, but it's really understanding how to tweak your product from an idea to solve a problem into something that fits into the customer's workflows and solves their problems. The only way to really validate the product is to see who pays money for it.