Why did Micro Center Sell my parts

My buddy went to Micro Center to buy his first gaming PC. We picked out all the parts and went to checkout. As he was checking out his card got declined because of the bank thinking it was fraud. The employees told him they could hold it until Monday when his bank opens in order to complete the purchase. He goes back on Monday to discover they sold three of his parts that were on hold for him. They sold his motherboard, Power supply, and graphics card. He ask the employees for the same parts but they were sold out. I do not understand why they would put something on hold and then sell it beneath him.