In my opinion, when creating an SFI advert, don't promise too much. Don't give the impression of get rich quick or instant income. Don't make it look like a magic wand to wealth. These will get you sign ups who will lose motivation after a few days.
Keep it real, as close to the truth as possible that a little work and dedication is needed to get one off the ground. And remember to point out that its a long term planning and not a short term program.