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>El sitio www.negocio-extraordinario.com recibe mucha publicidad aquí en Cochabamba. Debido a mi falta de experiencia con el fraude del tipo "esquema pirámide" ("pyramid scheme"), ¿podrían darme su opinión sobre si es, o no es, un fraude de este tipo? Sí que parece sospechoso.

It doesn't have to be a fraud to qualify for a pyramidal scheme - and this one has all the qualities to be both.
First, note the long, long introduction, with a bunch of hogwash, aimed to exhaust your attention. Repetition of their buzzwords, pictures of happy and wealthy people, the usual arsenal of timeshare sales and such.

A pyramidal scheme is whatever makes you money not by just sales, but by geometric expansion of the network. If they promise more money for expansion than for sales, that's it. They usually say the market is unsaturated, but you may never know how saturated it really is. If they refuse to publish the size of the existing network, it's probably spread already and there's nothing much left for the newcomers, except to earn someone referral fees.

Any geometrically expanding scheme runs out of participants after a finite number of steps. Those who start it do get the money; those close to them get some; those who joined in the 6th or later rounds may be lucky if they break even. Most of the participants are lucky if they don't lose much.

When I was a kid, it was still very naive - send a postcard to the top address, and send six postcards to the six addresses of your choice, passing a list of five addresses on each, omitting the top address and adding yours at the bottom. After a while you're supposed to get 7776 postcards. Never got one. Reason? If I was already at the bottom, it meant that I was one of the existing 9331 (7776+1296+216+36+6+1) people already in the game, which meant that the game should already need 60466176 (sixty million) participants to complete to the level where current level 6 players would get to the top.

Nowadays, it's money, but the theory remains the same.