Here's a rule of thumb I find works well: People are stupid. Heck, I should get a T-shirt made up that says that, except I'd probably offend even more poeple than that time I said my sites don't get penalized.
There's a forum in my niche where the sales people did a big thread on SEO. It was like you took DP and Warrior forums and mixed them together - loud AND stupid. Anyway they're actually ranting about publicly about how much a niche directory owner was making from listings. Being the helpful diplomat that I am, I pointed out that in the first month I'd made 7X what I'd paid for an annual listing. Then I called them a pack of idiots because they were worried about how much someone else was making rather than how much they were making (might have screwed up the diplomat part). I suggested that if I was going to worry about anything, it was how I could pay even more for a second listing.
But that's people for you, if they have to pay someone $1 in order to make $5, they get all worried that you're making $1. Many would rather save the $1, keep it for themselves. The fact that they'll have $4 more doesn't get on their radar.