telemarketing products are they good for health / cheating us?

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The telemarketing produts like increasing the hegiht, reducing waits etc show on TV whether they deliver the promises made. My friends who have purchased these product say that only some products are good. Is it true? whether prolong usage will lead to health hazads?. Is there any international quality certification for these products. Overall I gather the opinion that most of the telemarketing products are wastes/ cheats