The resale market is where the best value is, and where most of the fraud is. Three habits remove most of the risk.
Marketplaces protect transactions that happen through them. A seller who asks you to pay by bank transfer or message them privately is asking you to give that protection up. Decline.
Card payments generally come with a right to dispute a transaction if goods do not arrive or are not as described. The mechanism is known as a chargeback, explained in Wikipedia's article on chargebacks. Bank transfers, gift cards and cryptocurrency offer nothing comparable.
A genuine seller finds this mildly annoying. A fraudulent one finds it impossible.
Search completed sales, not asking prices. An item listed well below recent sales is either a mistake or a trap, and mistakes are rare.