all that glistens is not gold
Things that have an outward appeal are often not as beautiful or valuable as they seem. I don't know if that necklace from the flea market will have the resale value you're anticipating. All that glistens is not gold, you know. A: "I want to grow up to be a movie star, then I won't have a care in the world!" B: "Just remember that all that glistens is not gold. The pressures of fame can be difficult." Yeah, that car is exquisite-looking, but it's not very well made—my friend has one, and it's in the shop practically every week. Talk about "all that glistens is not gold."
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