There are many different types of pilings or underpinnings used in foundation repair. Not all pilings are effective in all soil conditions. Get several foundation contactors to look at the problem before you make your decision which company to go with.
Use a foundation repair company or professional that is used to the soil conditions in your area. Soil comes in many different compositions, and the repair will need to work with the soil base to avoid further complications.
Get a written estimate from the foundation contractor, ideally get several and make a comparison. Don't go with the cheapest company, especially if they are quoting a much lower prices. Experience and expertise is important in foundation repair, you don't want to go with someone that doesn't know exactly what they are doing.
