There are some slick and very shonky sales people out there lining up to rip you off. There are honest pest managers who just want to give you a good job at a fair price. Then there's all the rest. How can you decide who to employ?
Here's a few simple pointers. I hope they help.

1. The Need: Don't be rushed. Chances are you have plenty of time to consider your options. Take your time.  Consider how you know what you know.  Keep notes of all conversations and keep your paper trail..
2. The Business: How secure is the business? Does it have a bad name? Are they afraid to answer your questions? Does the mention of their name ring alarm bells at your local consumer advocacy/complaints group? Can they provide the names of satisfied customers as referees? Don't necessarily feel that big is better; a large company may turn out to be just loosely controlled franchises, offering at best no better service than the smaller competition. The quality of the job will only be as good as the person who carries it out. Will the person actually doing the work be well trained and knowledgeable and able to talk with you or are you dealing with a salesperson who can only provide the quotation?
3. Face to Face: Meet them on your own turf. Depending on the nature of the problem, many pest controllers will provide a quotation either at no cost or fairly inexpensively. They may be prepared to just turn up and talk with you while requiring a fee before they'll do any inspection. This is fair, as any information they provide on the basis of inspection whether free or at cost, implies at least some professional responsibility and hence potential liability on their part. Beware the "free" inspection. Everything has to be paid for eventually, by somebody, sometime.   Separate the inspection from the control proposal.  Make sure that you get a proper (on paper) timber pest inspection report and make sure that it identifies the pests as far as possible.
4. Safety in Numbers: Approach at least two or three businesses. Compare their advice and quotations. Decide whom you would best trust with your assets. Then compare prices. Beware the surprisingly cheap quotation. It is easy to do a cursory inspection and to excessively dilute any expensive chemicals, or just not apply them where they should go. Remember the value of a good warranty. Read Claire's experience. Know the different ways termites can be managed and why the one proposed is thought best for you.
5. The Fine Print: What does the paperwork look like? After an inspection, you should be handed a written report, usually with a site diagram and the problem areas at least approximately mapped. The information should be clear. If it is presented on a preprinted form, the notations should be informative and quite clear. Look over the warranty. How small is the fine print? Do they mind you reading the contract? Is the scope of work made fully clear and is sufficient detail present to enable you to compare and contrast the quotes?
6. A Relationship?: What about contracts? Are you just getting them to fix today's problem or are you signing up for a never-ending dependency? What if you sign and you don't want them back again? What if termites come back in one, two or three years? What will they do then? If they've done good work, should you pay a maintenance fee for the year on top of the other costs? It is always important to check value for money. Maybe that service contract is aimed more at maximising income rather than minimising termites? You have to work it all out. There's often comfort in a trusted name, but you should put at least as much weight on local people's experiences as you do on brand recognition. Don't get me wrong, sometimes service contracts are the way to go, especially with a baiting program where you want it all planned out and costed in advance.

Ohio State University also have some advice on choosing your pest controller. Then again, so do Texas A&M and in Illinois, the Department of Public Health.  Hope this helps. Please feel free to email me with your experiences.