Does the fence company use their employees to install and service their fencing?
There is nothing like a contractor knowing and trusting his Own Employees. Nor can it be minimized the importance of an employee completely understanding the expectations of his employer. In addition the fence contractor that "subs" out their work does not have full control over the sub as this subcontractor schedules his own time based on his own projects.
Does the fence contractor guarantee his work?
Beyond the manufactures warranty, the fence company should guarantee their labor for one year.
Ask friends and family
Many of your family members or friends have used fence companies in the past or have neighbors that have fences. Most will be more than happy to share their experiences.
Ask them all the same questions about their experience to get a true apple to apples view of the different contractors.
Get references from the fence contractor
Obtain and make sure to call several references from each contractor. Again, be consistent with your questions so you can objectively determine the pluses and minuses of each fence company.
How to Choose the Best Fence Company
Choosing a Contractor.