measuring ROI?

[humpo]

Local car dealer wants some SEO work done, would like to show them proof of ROI and not just the extra visitor numbers.

The problem is its difficult to know how many sales are generated from the website and how many from traditional marketing. Their sales are erratic, one month can be very good the next low, basically they can do better or worse depending on the weather. So unless they start getting a huge increase in sales that corresponds to a huge increase in traffic i can’t really claim to of helped their sales. (budget doesnt cover a huge increase :))

They have said they will ask customers how they found them , but i know them really well and can not see them bothering with this.

Is there an effective way of measuring their ROI?

[Bernard]

If they are buying on-line, you can track it. If they are buying in person after viewing the site, you have no effective means to track ROI.

[humpo]

Thanks!

Next best thing, anyone?

I’m guessing there must be some agreement between an SEO and the client on what will be achieved and how to measure it even for offline sales?

KW ranking?
% increase in visitors?
% increase in visitors for some KW words?

[bwelford]

They have said they will ask customers how they found them , but i know them really well and can not see them bothering with this.
As you say, other influences come into play on the final sale. Seems to me that if they were willing to accept the customers' word on why they came as proof, then they should be willing to accept your last suggestions on:
% increase in visitors?
% increase in visitors for some KW words?
Those to me sound like the best measure of your SEO efforts.