Is what the questioner did—repeatedly purchasing merchandise and returning it to keep it as a "gift" after getting a refund for its price—halal or haram?

If it is highly probable that the seller will refund the money a second time, then it is not permissible to purchase with the intention of retrieving the money and keeping the item; for that is deception and consuming people's wealth unlawfully. Allah Almighty says: "O you who have believed, do not consume one another's wealth unjustly but only [in lawful] trade by mutual consent." The jurists have held that the transfer of ownership requires consent and an intention free from defects of consent such as deception and fraud.