He promised clients a 50% profit within 45 days, or 100% profit within 90 days, by buying discounted postal reply coupons in other countries and redeeming them at face value in the United States as a form of arbitrage.
查尔斯·庞茲承诺客户在45天之内获得50％的利润，或在90天之内获得100％的利润，通过收购其他国家贴现的郵政票據，然后再在美国按面值赎回，作为套利的一种形式。