Well, tv is one thing, but real life is another. It kind of depends on context and how you say it. The phrase, "don't be fooled" doesn't necessarily carry disrespect (as I understand it from an american perspective) but depending how you use it, it could. For example, maybe at work your boss says to you, "You are so meticulous and organized with your work, your house must be spotless (clean)". And you respond, "don't be fooled, as soon as I get home I just play video games, my house is a mess!" that wouldn't come across as disrespectful, just office banter. But if your boss was asking you about hiring someone, and you didn't like that person and you said, "don't be fooled by this person's good resume! they know nothing about the job!" that would come across as condescending and disrespectful I think, since you're implying you understand better than your boss. You might tell an old person not to be fooled into buying a useless product they saw in an advertisement, or fooled into believing something untrue they saw on facebook. It's certainly not the same as calling someone a "fool" which is always disrespectful, but you should still be careful. Hope this explanation was helpful!

This is a good question. It depends on the situation, and also how you say the phrase. If you are suggesting that the person in a high position is stupid, then they will be insulted (of course). But, If it is clear that you are trying to protect them from a dangerous trick or a con-man, then you could say it to a person in a high position (the correct vocal tone would be important too).