Five secret Costco hacks from a millionaire businessman. One, to enter Costco for free without a membership, just ask a friend to buy you a gift card. Two, Costco loses money on rotisserie chickens and hot dogs just to get you in the door, so take advantage.Three, Costco often sells $100 big brand gift cards for just $80. It's practically free money. Four, if something you buy goes on sale within 30 days, Costco will refund the difference even without a receipt.Five, Costco offers a lifetime warranty, which ...