When going through a limo company’s web site, check for clues on the company’s qualifications to provide good service. Look for telephone numbers instead of mobile phone numbers, make sure that the website is registered under a company name instead of just an individual, and of course check for an actual address instead of a PO Box. These are to a certain extent evidences of that limo company’s professionalism.
A telephone call can also help you in making a decision. A telephone call operator’s manner in handling your questions provides you a measure of the professionalism of the limo service. Was the operator gracious? Did s/he answer your questions respectfully? Did she seem to know the answers to every question? If not, how did she handle questions beyond her responsibility? Did you feel that you can trust him/her?
You also have the choice of going for a broker. They are quite useful as they can do all the dirty work for you. However, consider that since they get paid for every inquiry they hand in or a commission for every successful limousine rental. So to speak, they have a vested interest on the matter. If you would like to go through this because it is easier, just make sure that you are aware of not only the benefits, but also the risks in having to deal with two separate units, the middleman, and the limo company.