Naofumi: "You got the rest right? You just have to sell it expensively while warning whether it helps or not depends on oneself. With just this, they’ll be happy to pay. Then if you spread rumors about how much of an effect it had on the customer who bought it smiling, more customers will come."
The probability it will go perfectly is very low, but the first part will likely succeed.
That the island's in the activation period means experience points are increased. Even if leveling up goes faster than usual because of the activation period, people will think maybe the accessories’ rumors are true.
Afterwards, observing the numbers and ability of the incoming adventurers will cause wishful thinking.
Swindler: "I will go get to work immediately!