Sometimes it’s not clear.
Walking into a doctor’s office and seeing an overweight doctor works as hidden advice from the doctor. Patients will trust his recommendations less and are more likely to switch to another, healthier looking, doctor. The patient’s health is at stake so why take health advice from someone who’s not taking it themselves, even if the doctor’s recommendations are spot on. We tend to hear what we see.
Sometimes there’s no choice.
“Does this dress make me look fat?” is usually hidden advice that a complement or, at the least, some reassurance is in order. The continuation of a smooth relationship is at stake. By coming up with a good compliment about the dress, you’ll be truthful because if she does look fat, it’s probably not the dress’ fault.
Sometimes it’s easy.
In certain situations people will be diplomatic when offering hidden advice through other channels. So if someone offers you a breath mint, take it.