There are many different types of electrical contractor, many of whom will provide great customer service and really know what they are doing on site. However, each electrician or contractor will have their own specialism, so if you need a large commercial job completing, it is best to contact a commercial electrical contractor. They will be used to working on a larger scale and will be more adept at overcoming problems in these types of properties.
Safety is, of course, the most important aspect when working with electrics. Contractors must know commercial properties and have a full understanding of the regulations that must be met. If you work in a specific industry, find contractors with experience in your field and area.
If you find a good electrical contractor, keep using them. Check whether they outsource or subcontract because this will affect whether you will be getting direct service from them.