I have the item Red Flute in PKMN White and the descriptions says " A toy flute made from red glass. A maniac will buy it for a high price. " Where is that maniac?
In undella bay go to the huge mansion on the left of the town , the riches mansion . Inside there will be a man similar to a karate guy and he will buy it for 7500 Pokedellars .
Its the same man that buys the relic items also .
Enjoy your 7500 PokeDollars.