2. Longevity: One of my favorite questions to get asked is "How long have you been in business?". I know that there are many quality SEOs out there that have been doing this stuff for far fewer years than we have, but I know that being able to tell people how long we've been in business is a considerable source of comfort for them. Longevity lets them know that the SEO is not some fly-by-night shop likely to cut and run or go out of business overnight.

3. Trust: There are many indicators of trust on a website and I know this plays a role. One of those symbols of trust is belonging to certain associations such as the Better Business Bureau. Displaying such symbols on the website serve to reinforce trust aspects, including longevity mention above.

4. Assurances: I was going to say guarantees here but I think people are starting to realize that top rankings cannot be guaranteed. Heck, even performance guarantees are hard to come by unless the SEO maintains virtually total control over the site's marketing aspects. We often get asked if we provide a guarantee only to find that the prospects are relieved to hear that we don't provide any top ranking guarantees. That answer gives them the assurance that they are looking for. These prospects are the ones who know to run away when promised a guaranteed #1 ranking in Google in 19 days.