If you are looking for a PPC Management agency there are a few things you need to look for.
First and foremost you should ask for references. Or you can look on the PPC Management agency's website and there should be a list of previous customers. Any ppc marketing companies that lists it's prior customers knows that they did an excellent job with their customers. If the list is on their website, they know that a potential customer may contact one or more of their previous clients.
If you see the previous clients listed on the PPC Marketing Companies website, go to a search engine and Google them. Check out where their previous customers rank online. You may want to try Bing and Yahoo search engine networks as well.
Make sure you choose a PPC Management agency that does not get you all excited and promise to rank you on page one of Google, Yahoo and Bing within a week. No company can do this as it takes time to build your rank on these search engines. An honest PPC Management Company will let you know that it takes time to work one's way up on the search engine rankings.
Also, depending on what type of business you have, will depend on how high of ranking you can achieve within a certain amount of time. The PPC Management agency should be able to give you an estimate on this question.