Back in the day, when I was studying marketing (not sure if this stat has changed?) but the rule of thumb was to put your "ad" in front of your "audience" seven times. I know a recent study shows that the average person holds an attention span for seven seconds and will wait approx no longer than 30 seconds for a web page to load (my younger sister is going to college right now and this is what they're being taught, so that's the basis of my info). Irregardless, I wouldn't waste my time with anyone that put my offer out only once. I think it was Joe Vitale or Mark Joyner that had talked about the "brainwashing technique" (way back when) with repeated mailings, but just worded differently, so people would initially think you were talking about something else, but in reality they were just given a different of looking at the same thing, thus them not hitting the delete key upon receipt of the "sales message".