Heck - if I really wanted to work for them and I had the background you do - I would email them a resume. I think their blurb on the website, like Flash said, is more to weed out the people who email them saying they are "MSPA Gold Certified and have done 500 gas station shops and are ready for hotels!" then to weed out people such as yourself.
Can I ask why you want to work with them specifically? From looking at their website it seems like basically they do integrity focused evals and are more PI then "mystery shopper" or customer experience focused. That personally is not my cup of tea, but maybe I am missing something.
Also, do know that many clients (at least half if not more) on their "client list" have active shopping programs currently with other MSPs, so if it is that which is driving your desire to get in with them, recognize that there are many paths to your desired objective.