Is it permissible to exchange a piece of clothing after a small part of it has been wet with water at home, without informing the seller of that?

If the wetness of the clothes leaves a mark that diminishes their value or lessens buyers' desire for them, this must be disclosed to the seller before exchanging them. If the seller agrees, there is no blame upon you. However, concealing this is forbidden deception, and "whoever cheats us is not of us," and "cunning and deceit are in the Fire." Exchanging clothes is considered a sale, and any incidental defect that the seller would dislike if he became aware of it must be disclosed, even if it is merely a suspicion. For "if they are truthful and make clear, they will be blessed in their sale, and if they lie and conceal, the blessing of their sale will be erased."