Why that method can convince people? It's because we don't want to look too much, because in the fact, we're not also get (for example) $500/month right? That must be a fluctuations, so instead to write $500, i think it's better to write $100-$500. Or maybe if the range is so far, we can make it become $300-$500. It's honest and still interesting
Or do you want to tell people, the max amount you ever get?