Consistency is key in designing presentation visuals.
It is tempting to use a variety of fonts and colors to make a presentation more appealing to an audience, but changing fonts and colors from slide to slide is actually quite distracting. Developing page layouts and a color scheme and adhering to them throughout the presentation will keep the audience focused on the speaker's message, not on what font the next title will be in or what background color might next appear. A good rule of thumb for fonts is to keep sizes, colors and placement consistent. Try to use no more than three complementary fonts in a presentation, i.e. one for titles, one for subtitles and one for text and graph labels. While service bureaus have a great number of fonts available to them, they may not have the specific one you have selected to use.