I'm not an expert, but I make 'em. Seriously. In the comments, someone asked me what I do for a living. I'm a medical writer--at least until I get into a philosophy PhD program. You might also call me an expert farmer. Not as in someone who has farming expertise, but as in someone who farms experts as part of the vertical integration of big pharma. It's a sort of genteel plagiarism, really. Each firm has a marketing team to pinpoint high-prescribing doctors with academic aspirations. (Maybe one of these days I'll blog about how they drug companies know who prescribes what. It's very creepy.)
These days it's very chic to recruit high-prescribers for the medical equivalent of the Tupperware party. These events are known as "lunch 'n learns." The doc gives a half-hour talk at the local hospital, the company supplies monogrammed bagel caddies and tubs of cream cheese. The company writes the doc a check for upwards of $1000. Where do busy clinicians find the time to make their own polished PowerPoint presentations? They don't, I do.
I can assure you, the company gets their memetic money's worth. The same slides will be repurposed for continuing medical education modules, conference talks, and even reviews for medical journals. I might add that these reviews often bypass peer review because their ostensible authors are such big experts. Thankfully, the experts sign their names to the commercials and not me.