There seems to be quite a lot of discussion in the blogosphere about how to select a search engine optimization firm. While it is of course necessary to see first hand proof of results the firm you select has produced for clients, SEO is such a complex industry that there are a few questions you must ask to get a handle on not just overall approach but style.
Investigate Link Building Strategies:
Link building is essentially the core of "best-practice" SEO, which means that it is important to make sure that they give enough time to the effort associated with building IBL's or inbound links. Find out what strategies your SEO uses and research the impact they have on listings. As always, avoid link farms and do not break the bank on buying links from other sites.
Assistance in Improving Conversions:
There is a reason that many businesses select firms which provide a suite of services - they have more tools at their command to help you enhance conversions. For example, an pure SEO provider may be able to get you loads of qualified traffic but the conversions you generate may be low as a result of poor design. If you select an integrated online marketing firm, they can assist you with copywriting, and defining usability issue to name a few. In the end, the name of the game is getting the most conversions possible from your Internet marketing efforts so always make sure that the SEO firm you select is more concerned with conversions than the actual number of visitors they send or the placement your listing receives at search engine.
Availability or Openness to Proper Measurement:
There is simply no replacement for natural traffic (the traffic generated through non-sponsored listings on popular search engines (such as Yahoo, Google, MSN, AOL or the slew of others in the market) and only qualified SEO's can generate such traffic. If you are concerned about how your SEO is measuring up and want to determine the effectiveness of marketing campaigns managed by an outsourced SEO, make sure you have access to server logs in order to see not only the amount of traffic but where it is coming from and via what keywords.
Also consider utilizing a third party return on investment conversion tracker which lets you measure the effectiveness of individual campaigns - such as SEO, SEM, PPC, link exchanges, banners - from any location where a click can be counted. It works by appending the URL with a special alphanumeric code and inserting tracking code within two locations of your domain - typically a landing page and a page which indicates a successful conversion. Two such services are ConversionRuler.com and ROIspy.com.