How to quantify or justify ROI

I have been thinking a lot lately of how to exactly quantify the value of my work.

Bearing in mind that the client wants the best possible ROI, and organic SEO is the way to go with that, and the Investment is how much the SEO gets paid.

The return is the amount of business generated from the work.

The problem with this is that that amount can't be directly correlated to the SEO work done and the SERps achieved. A high SERP means nothing on its own if the web site doesn't work properly, has a bad host and lots of down time, is un usable etc!

In this case the SEO work could have been top notch yet the ROI could be quite low still.

How do you quantify the value of SEO work and under what conditions would you turn down a job?

I am considering putting sites through a vetting process, partly to cover the reasons above and partly to help generate additional work in "fixing" problems with sites before any SEO starts.

Value of the work you do for client is measured by the client, how much they value what your doing and believe it will help thei rbottom line. That means you have to decide how much your work is depending on what the client wants/pays. More time = more money, more investment by interested clients = more money. You should have a generally standard clear accross the board that is only dependent on time. Its' too hard to measure the rest.