As a nonexpert user let me suggest you break it down as you would in choosing a physician for your healthcare.
Some of this you have to do yourself. You don't need a doctor to stop bad habits or start good habits. You will make the final decisions, and you probably suspect where your system is not healthy.
Then you have to choose a local provider, so word of mouth is the best way. Who are the other offices using, who are the other AC users using, who do the hospital IT recommend from your list. Whoever you choose should be successful. You pay a little more for peace of mind, and who wants to pick a doctor that will be leaving town or changing careers soon. Small office IT work is hard because everyone wants something for nothing. It may be hard to get the help you expect, and you may have to have more than one for different types of problems.
Then you have to realize that IT is complicated and there can be problems. The healthier you are the more you can expect perfection, but most of us are old enough to live with some imperfection, just like with AC. Every IT person makes mistakes or has complications just like every doctor does. How often and how do they respond to it is important. Leave an IT provider just like you would a doctor, not at the first problem, cause the relationship is as important as the process. You are paying for the ability to move to the front of the line when you have a real emergency, and sometimes you have to wait for someone else's emergency.
Then you have to decide if you need to go outside of town for the right expertise. Just like do you want to go to the university hospital for your surgery? There is amazing expertise available here and out there that is worth every dollar you pay to get it right.
And if something doesn't work, ask your staff if they rebooted their computer.