If the writer is looking for someone to draw their idea for them, then it's not a "team effort" in the same sense that a two people coming up with an idea together is, so it's only natural that it should feel different.
If a writer doesn't like creating a comic via a business transaction, well then they had better learn to draw. The chances of stumbling across an artist who both wants to be their friend and to dedicate themselves wholly to the writer's idea for no payment are very small, and it's an unreasonable expectation to have of someone.
Sucessful collaborations with no money involved tend to happen between friends, often people who have roleplayed together. They create a cast of characters and a world that they have both contributed to and become invested in, rather than one person supplying the story and the other the art.
As for the commissions issue, I don't think it's standard practice to sell prints of commissioned work without the client's permission, so it sounds like you've come across some unscrupulous artists. If it's something you're concerned about, you should bring it up with the artist beforehand and get their written agreement, or take your money elsewhere if they don't like it.