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The ETH that you would send to the address to fund the token transfer (e.g. $20 worth of ETH) will be stolen by the scammer (minus e.g. a $2 ETH TX fee). The scammer pockets the remaining $18 because as I mentioned above "pure" ETH TX fees are much lower than token TX fees.
Thank you for clarifying, that's a really hideous scam if you think about it, it's making you waste your time and you also don't get anything. Not to mention that these scammers have stooped so low that they're happy stealing measly amount of crypto.