Trust me

If the speaker is someone who you already trust, telling you to have faith in their ability to accomplish a certain task or get through a difficult situation, it's a different story. But if "Trust me" is implicitly followed by "with your well-being/money, even though you don't really know me", then what the speaker really means is... well, I guess leonfp put it pretty well.

Other phrases which are also generally bold-faced lies include:

• " I'm a man of my word"
• " It's not about money"
• " The check's in the mail"
• " I'm not gonna spend it on booze"
• " We'll fix it in the mix"
• " We care about you, the customer"
• " We're the best in the business"
• Any opinion offered by salesmen
• Most anything out of the mouth of an actual politician