The real problem is trusting the information you receive. In this case, you must at least authenticate the person to whom you receive the information. The question is good, but for really good solutions you will need to consider ranking algorithms.
They work a bit like Pretty Good Privacy (PGP), where trusted relationships are distributed and used to authenticate the recommendation chain. There are many academic studies on this subject:
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ISBN: 0-7695-1993-8.
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6, 1/2007, . 40 - 55