If a snake oil salesman scams you out of dollars, what do you call that? A dollar scam or a snake oil scam? If a scammer asks you to send bitcoin in exchange

If a snake oil salesman scams you out of dollars, what do you call that? A dollar scam or a snake oil scam? If a scammer asks you to send bitcoin in exchange for xyz which is never delivered or worthless, is it a Bitcoin or an xyz scam?