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The Australian salesman flashed up a slide of a black Rolls Royce and pitched enticingly to a roomful of Vietnamese students facing an uncertain economic future: join me in selling anti-aging products and the car — and much more — could be yours in just a few years.

It's a simple formula that has worked well for the company, Nu Skin, which has stormed through Asia over the last two decades, racking up huge profits despite regulatory scrutiny over its marketing practices.

Vietnam is the latest frontier for the company, launching at a time of stuttering economic growth and rising bankruptcies.

That would hold back many consumer companies, but for multilevel marketers it is not necessarily a problem. Selling a cheap business opportunity is easier in troubled times.