First, most “Professional Engineers" (P.E.) are independent engineers and are not obligated to promote a particular foundation repair company or it’s product. However, the typical salesman/engineer that works for a foundation repair company can only sell the pier product his company installs. 

Another reason you should hire an independent engineer (P.E.) is the simple reason that foundation repair companies are in the business of selling piers; fact is, piers are not always the best solution to every foundation problem.  An independent engineer has the latitude to consider solutions beyond merely installing piers. Independent, professional engineers aren’t paid by commission, nor are they tied to a specific repair methodology.

Finally, before a repair plan can be developed for a foundation, it is necessary to first analyze why the foundation is moving. This requires an understanding of the various soil conditions in the DFW region. Among a variety of other subjects, structural engineers have received formal education in Soil Mechanics and Structural Analysis.  Preferably, the structural engineer you retain not only has received a formal education but also has broad experience dealing with North Texas soils.