I have had at least 5 different SEO developers after the Google Panda and Penguin came out. The first 4 I hired from the Philippines, paying them roughly $500 a month, to which all we had are failures. The last one we hired is from the U.S., paying them $1,000 a month, and after being with them for 6 months, we hardly got any improvement. They were a reputable company, part of the Inc 500 fastest growing companies.
Now, looking for a new SEO developer, what are the factors I should look at to determine if they are capable of delivering results?