When you have an online business you do not have the perks of selling your product in person. Therefore, your words are very important; they make or break a sale. Writing up a sales letter means getting into the minds of your readers. You should know who your customer base is, what age group, gender, etc. You need to use psychology and tactics that will draw your readers to buy immediately. Your sales copy should be captivating so that your customer is interested in reading through it, however long it is.
Some sales letters are twenty pages long, but still keep the readers attention the entire time. The sales letter needs to fully describe the problem the customer may be having and why your product is the only solution.