This page of our guide to Animal Crossing New Horizons describes Redd, a very unusual and somewhat dodgy salesman who offers pieces of art.
Redd is a mysterious guy - you better watch out for him. At first, he will approach you a few times and offer a painting. Agree, and eventually he will find himself a safe cove in the northern part of your island. Visit his ship from time to time to buy various pieces of art. Unfortunately, only one of them will be genuine - the rest are fakes.
When does he show up?
Redd appears on the island on random days.
Where to find him?
Initially, Redd will be hanging around the island. Once you've done your first business with him, he will stay on the beach in the northern part of the island.
What can he do?
Redd sells art - paintings and sculptures. You can return the originals to the museum. What about the fakes? Blathers won't accept them; however, you can use them to decorate your house or its surroundings. The differences between fakes and originals are sometimes so subtle that no one will notice the difference - this way you will be able to have an almost authentic Mona Lisa hanging on the wall.