I had a mentor who trained me in the business. He was old school and did things a bit differently than we do today. A big part of his business was the pest control division. I ran a route for him and he paid me for the new clients I was able to develop. I still remember to this day what he told me. He said, "Blair, Every tree needs to be sprayed". And then he said, "Every yard needs a service at least every three months!" Being the young man that I was, I believed him. I sold route after route and made good money.
Selecting the right tree service to meet your budget and tree needs is not always as easy as it might seem. A complex may contract with three of four companies before it finds one that it is happy with. Asking questions about the company and it's work before you contract will save you some future headaches. Are there ISA Certified Arborists and/or ISA Certified Tree Workers on the crews? The ISA (International Society of Arboriculture) gives exams for these qualifications and sets tree industry standards accordingly.