I do if the money is right, and if you have enough experience you can predict the timescale. If you have been in SEO as long as I have you will learn that it is all about resources. the more resources you have the easier page one is.
Resources cost money. The more money clients pay the quicker you can utilise those resources.
Be under no illusion that Google takes it time 4 weeks turnaround on events is how most clever SEO's will work. 12 week to gain page one is not asking for much if the client is willing to pay.
Like many good SEO's we dont do cheap prices because we know the work involved. We are however cost effective.
EG. I quote £2000 you quote £500, you get him to page one in 12 months, I get him there in 4
Using me cost him £8,000 using you cost him £6,000, so you saved £2000.
Now you may be sat there thinking Why should you use me (or other SEO's who quote like me). Its simple. TIME is the most expensive commodity out there. Once it is used up it is gone and there is no way of getting it back.
With my SEO you will still have 8 months of extra time on page one of Google.
This time allows for reputation to be built and word of mouth to be generated. 8 months of "zero" business is a long time.
Next time you spend on SEO think, you cannot accumulate if you dont speculate.
I don't know how any of you can quote timescales regardless of how much money is invested, ultimately the decision is in the hands of Google and no individual or company can accurately predict any kind of timescales.