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The main method of recruitment appears to be the very same as recruiting porn actors of both sexes in the U.S. of A,.
Billyboy12... we've all seen those
"Be a Model" newspaper classified ads.
Perhaps these ads are more upfront in Japan, spelling out the porno nature of the job, instead of the "Bait and Switch" technique used in America; particularly regarding ads in Japan that cater especially to men, implying such ads can afford to be honest... assuming the social mores in Japan are more relaxed with sexual matters. The ads in America try to weed out the more open-minded or desperate women; from what I have read, Japanese smut peddlers use talent scouts for the ladies, hunting for new talent off the streets.
Fellow with the blurred face is from a shoplifting video; see how Extraordinary Electromog came up withhttp://www.akiba-online.com/showthread.php?t=1341986 the identity of this movie, and several others. They probably didn't go far enough with this man, as his features can still be made out.
The background male actors are referred to as "soup men," and they are regular guys... and as you surmised in your ending sentence, their incentive is to appear in JAVs, big fans as they are. They do get paid, but as little as ten dollars (or 1,000 yen), to begin with. Their main condition is not to get recognized, which is why we often get the mosaic on male faces.
Above is from an uncensored shoplifting video; sometimes the JAV makers go overboard with their mosaics, venturing dangerously into erection-distraction territory.
I learned about mentioned ins and outs from an article, which I put up in
Akiba-Online's news section very recently; see "Article Three":
http://www.akiba-online.com/showthread.php?t=1337260
By the way, the "average appearance" of the soup men is not necessarily an indication of their amateur status, is it? Given the appearance of many Japanese porn actors who have reached the elite ranks, such as
The Creep and The Bad.
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