Mavis Discount Tire review: Tire replacement

I went to mavis with a low tire pressure on a tire. They changed a tire and then i still had low tire pressure. When i returned they said the low tire pressure was becasue of a cracked rim. When I asked them to put back my old tire and refund my money they said they're not responsible to check cracked rims. Really can't you at least check the tire and see if it has a flat?