As an agent, I LOVE when a client can identify his/her most important customer-service criteria, i.e. "phone replies within 12 hours, e-mail within 24," etc.
Find a Realtor who has a present-day track record of sold listings, and feel free to ask for (and check) references, i.e. recent happy clients.
If an agent is "honest and direct," it's more valuable - - - in reaching your goal, at least - - - than strictly "charming & complimentary." Realtors strive to be ALL of those things, but sometimes the top producers aren't the sweetest . . . but who ARE most able to help sellers truly study, understand, and ENGAGE in the most effective steps - - - even if painful or inconvenient - - - that result in a closed sale.
Kerry is right: Keep in mind that a good professional agent can "only do so much" if the property is overpriced, inaccessible, beset by neighborhood problems (curable or otherwise), or if it presents repair issues that obstruct regular financing.
Ultimately, in my experience, there is always a buyer...but buyers are better-educated than ever before, and their decisions are ruled by VALUE over all else, regardless of the neighborhood, price segment, or quality level they seek. Once you know that your property is as marketable as possible, and your agent is working at 100%, don't wait long to adjust the price unless you're getting action.