Tips when selecting an SEO:

• Always check testimonials. Ranking results should be displayed in a format where they can be checked by simply clicking on the keyword. If not, copy and paste into Google and look for the associated domain name. Go to the website concerned and ensure that the SEO or web design company is the one that is providing the optimisation. This is generally situated on the clients website footer.
• Try to avoid companies who offer no guarantees yet charge a fortune. These companies may or not be on page 1 or 2 on the search engines.
• Just because a company is on page one of Google under 'search engine optimisation' does not mean to say they will obtain the same results for your website. Ensure you know what you are paying for.
• Avoid companies who use sponsored links to promote organic SEO. UNLESS! They provide testimonials and good ranking results for genuine clients. There is nothing wrong with this. It maybe that they are too busy looking after clients interests.
• When contacting a search engine optimisation company, ask if they optimise and prepare the whole website. Listen for background noise and if it is awash with a room full of sales people - whatever they say get it confirmed in writing.
• Avoid the heavy sales pitch. Generally easily spotted by the above, an avoidance of answering direct questions or a repetitive sales pitch, but we are on page 1 position.  

The moral of the story is:

• Try to use an approved search engine optimisation company that specialises in whole website optimisation, provides 100% search engine website architecture, all URLs are 100% search engine friendly and one that provides back links to deep pages as well as the home page as part of their seo package. This is very important for ecommerce shopping carts if all products are going to attract page 1 & page 2 listings.