Ask three questions before signing. When did the agency last use Google themselves, and what did they do with the result? How many of their own customers found them through search in the past year? And what would they build for you if search traffic halved again? My own numbers after doing the SEO job properly: thousands of cross-links and new landing pages brought maybe 2.5 to 5 percent of the views, with 1.55K impressions in three months at an average position of 25. Google saw the pages. People did not come. The answers to the three questions say more than any proposal.