Ideally before you get any SEO paid for you need to know what the likely yield is, the amount, and strength of your comp.
This means knowing the number of clicks per day on your chosen keyword, how well your comp's site is optimised and the quantity and quality of their backlinks.
If I bought SEO work I would base it on clicks rather than position, but I doubt they woukd be interested cos there is so many easy pickings out there for people who haven't got a clue.