In just a few minutes, one art collector may have earned more credit card rewards than most people will in a lifetime. Billionaire art collector Liu Yiqian paid $170.4 million (one of the highest prices ever paid at an auction) for Amedeo Modigliani’s “Nu Couche” on Monday. He plans to pay for the painting with his American Express AXP, +0.08% Centurion card, a card for high-net-worth spenders that has no official credit limit, according to news reports. Last year, the same collector purchased a $36.3 million porcelain cup, reportedly with his American Express Centurion card, Bloomberg News reported at the time. ... (full story)