When searching for someone to work on your valuable property it is so very important to make sure the company is licensed and insured. Tree trimming and especially tree removal is one of the most dangerous professions in the world, it should not be attempted by anyone that does not have years of experience!
Here in Colorado Springs all licensed tree services have been vetted thoroughly by the City of Colorado Springs before they are issued a license. Owners are required to pass a written exam as well as perform a test climb to prove their knowledge of proper tree pruning techniques. Most importantly they are required to have the proper Workman's compensation as well as Liability insurance. You can find a list of local licensed tree services at the following website, coloradosprings.gov, and then visit their forestry page. We at Affordable Tree encourage people to get competitive bids from other reputable companies.
When it comes to disease and diagnosis, make sure that the company you are dealing with is licensed by the Colorado Department of Agriculture. Only companies with this license are allowed to offer chemical treatment of insects or disease. Some companies will say they are a full service company but without this license they are not truly qualified to treat your trees and shrubs. Once again if they are a commercial applicator, licensed by the Department of Agriculture, then they have been thoroughly vetted by the State of Colorado and have the proper credentials to perform the work requested.
So take your time, get competitive bids, know the credentials of the person you are dealing with!