Search engine optimization is one of a kind consultation projects which we can hardly measure the results, in order words the yield is abstract and it becomes harder to achieve customer satisfaction.
You may consider some of the followings as benchmark:
- Rise in Google Pagerank / Alexa rank
- Rise in the actual ranking in SERP
- Increase of visitors as on traffic statistics
- Goodwill as shown in social web sites like Digg, StumbleUpon etc.
On the other hand the followings may pose controversy or uncertainties in measuring the deliverables:
- Sustainability of ranking (Pagerank or SERP)
- Potential damage in reputation caused by suspected black hat tactics
- Users efforts involved to sustain the ranking, if in case not clearly stated in the beginning
- Difference in rankings as shown in local search engines
SEOmoz has given good examples in formulating the disclaimers and other relevant clauses in the service contract to protect SEO consultants, or allow them to have a better prior communications with their clients when aligning their expectations. Given the following example as quoted:
SEOMOZ MAKES NO WARRANTY, EXPRESS, IMPLIED OR STATUTORY, WITH RESPECT TO THE SERVICES PROVIDED HEREUNDER, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTY OF RELIABILITY, USEFULNESS, MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, NONINFRINGEMENT, OR THOSE ARISING FROM THE COURSE OF PERFORMANCE, DEALING, USAGE OR TRADE. By signing this agreement, you acknowledge that SEOmoz neither owns nor governs the actions of any search engine. You also acknowledge that due to fluctuations in the relative competitiveness of some search terms, recurring changes in the search engine algorithms and other competitive factors, it is impossible to guarantee number one rankings or consistent top ten rankings, or any other specific rankings for any particular search term.
The following is an example of an Opportunity to Cure which allow a buffer for consultant to fix a problem before ending up in a litigation.
Opportunity to Cure. Prior to any claim for damages being made, you must provide SEOmoz with reasonable notice of any alleged deficiencies in performance and SEOmoz shall have a reasonable opportunity to cure any alleged defect in performance.
Same as other kinds of service contracts, SEO consultants should employ careful provisions and clauses in the contracts as a more integral agreement with their clients. Such reference would be particularly useful given SEO as a relatively new kind of business.
Some reference links as provided below: