We aren't huge proponents of using the RFP process to find an SEO agency, but if you've been dealt that hand, we're here to help. That's why we've provided this free SEO RFP template.
There are many aspects of selecting the right SEO agency that an RFP simply won't give you such as the opportunity to ask hard results oriented questions and experiencing the personalities of the people that will be working with you.
There are also a few good reasons to use an RFP for SEO. You should be able to sort pretty swiftly through the companies that are "selling SEO" more than they are actually practicing it. The telltale signs of this are SEO RFP responses that talk about heavy link building, ranking reports and "content written for search engine algorithms." If you see those items emphasized you've likely gotten an response that you can pass on.
Things we would expect to see in an RFP response provided by an agency that really understands search engine optimization would include things like content and UX enhancements to make the site more valuable to the user as well as a team that includes writers, creatives, developers and search optimization specialists. These are indicators that while the agency likely provides true search engine optimization services, they understand that that means making your website better for users.
We always recommend taking the time to meet face to face with your finalists. Take the time to gauge personalities, see and understand their past work and get a feel for how they would approach your site and unique business needs.