Hi Freedom,
They only work till they reach the saturation point, which might not take long if you live in an area with a small population, say under 50,000.
But you are right about one thing, success will be directly proportional to the amount of effort put into it.
It also helps if you get into it at the beginning, while there is still growth potential. Once one of these schemes has been around more than a year, it's probably too late by then.
Jrig