While I haven't used Accessfares,,, they seem alright.... I have used Cooktravel.net which is affiliated with American Express.

They are very upfront about what they do. They have called an airline and gotten me an upgrade from a full coach fare which saved me $3,000.

They also give back annual Amex rewards on almost any fare which cuts the price by a couple of hundred dollars on even published sale fares.

They also have a number of net and consolidator deals for business and First.

I think there are a couple other agencies that do the same thing,, but my best experience is with cooktravel.net

Best to call these type of agencies during business hours.. they get their deals because the airlines have empty seats and don't want to dilute their published fares in a public way.

Good Luck