I had seen some of Mariana van Zeller's work on the defunct Current channel and been impressed. Here is a sign she's doing just as well at National Geographic.In this program, the Portugal-born, scarf-wearing documentarian takes a look at escort services along the Strip in Las Vegas. She talks to sex workers, their employers, casino staff, cabbies, and activists -- practically everyone who could be involved except for the johns (an unfortunate omission). We're told that those hyper-sexy, scantily clad women we see in casinos often are hookers who ride up and down the hotel elevators turning tricks with guys who haven't yet lost their shirts. We eavesdrop on one exchange in which a gambler asks a busty casino-floor walker for a $600 "full-service" experience. Apparently he's low-balling; she walks away. We're told that sex workers often dislike their work, get roughed up doing it, and frequently end up with symptoms of post-traumatic stress disorder. What they do falls into a gray area of the law. As one escort who has written a book about the trade explains, "I don't have sex with men for money. I spend time with men for money. The sex is always free!"One prostitute discusses how the oldest profession will always be around. Men have biological urges that must be met, and if they're not getting what they need at home hookers are a "safe" option -- the guy can have fun and the hooker will never nag him to marry. Van Zeller gamely takes a hidden camera into one escort agency where she inquires about seeking work, and a male producer of hers goes undercover to ask a cab driver how to hook up with "a lady." He gets a wealth of information.This show is full of interesting characters, from egregiously silicon-enhanced sex workers to sleazy behind-the-scenes operators. We hear from one ex-prostitute who now has a street ministry aimed at converting sex workers to other ways of life. There's another former hooker who delivers lectures to men who have been arrested for soliciting sex. Excellent work by van Zeller on a subject that is much more complex than it typically is given credit for.