Probably one of the best pieces of advice I can give for anyone selling in any field, especially SEO, is to always under promise and then over deliver. A very quick way to impress a client, ensure client retention, and promote referrals from them is to promise them a mule and give them a stallion. This isn’t to say sell yourself short, however, when you are selling SEO, there are many variables that you cannot foresee. Make sure the client is well aware that ranking for their keywords might be difficult and take some time. If/when you start ranking and send a lot of traffic much more quickly than promised, the client will be thrilled. Don’t just use this advice on the initial sell. Continue to set expectations below what you think you can deliver. There is nothing worse than giving the client a expectation that is never met. If this happens, there is nothing worse than constantly trying to get out of a hole you dug for yourself.