Is it permissible to keep counterfeit clothes that were purchased without prior knowledge of them being counterfeit, given that there is no return policy? And is it generally permissible to purchase counterfeit clothes as long as the law does not prohibit it?

If a seller deceives a buyer and sells him a product that does not match its description—for example, selling him a counterfeit item as if it were original—the buyer has the right to annul the contract and get his money back, or to waive his right and accept the product. The principles of Sharia obligate restitution in cases of deception and fraud, and this is more primary than restitution due to a defect. Scholars have explicitly stated that deception is presenting the sold item with a desirable characteristic that it lacks, and in this case, the buyer has the option [to annul the contract]. As for selling counterfeit goods, there are two scenarios: The first is when the seller deceives the buyer and makes him believe it is original, and this is forbidden. The second is when the seller informs the buyer that it is counterfeit, or the buyer is aware of it, and there is no harm in this. However, the buyer should not purchase counterfeit goods to avoid assisting in the spread of fraud or infringing upon the rights of original companies.