Scammers will try to convince people to buy a "new token" that they've created (which has essentially 0 value) at x cost and hold. They continue selling the token to other people also. When you finally go to sell said token, it's still valued at 0 because no-one is trying to buy it at this point - there's no market. So you're stuck with it, and have still paid x cost. When they sell many of these, they make a huge profit - which is why they'll spam people with it.