From Appendix III of the rules of golf on Amateur/Professional status
3-1. Playing for Prize Money
An amateur golfer must not play golf for prize money or its equivalent in a match, competition or exhibition.
Note: An amateur golfer may participate in an event where prize money or its equivalent is offered, provided that prior to participation he waives his right to accept prize money in that event.
(Conduct contrary to the purpose and spirit of the Rules - see Rule 7-2.)
(Policy on gambling - see Appendix.)
3-2. Prize Limits
a. General
An amateur golfer must not accept a prize (other than a symbolic prize) or prize voucher of retail value in excess of $750 or the equivalent, or such a lesser figure as may be decided by the USGA. This limit applies to the total prizes or prize vouchers received by an amateur golfer in any one competition or series of competitions.
Exception: A prize, including a cash prize, for a hole-in-one made while playing golf may exceed the above prize limit.
b. Exchanging Prizes
An amateur golfer must not exchange a prize or prize voucher for cash.
Exception: An amateur golfer may submit a prize voucher to a state or regional golf association and thereafter be reimbursed from the value of that voucher for expenses incurred in participating in a golf competition, provided the reimbursement of such expenses is permitted under Rule 4-2.
Note 1: The responsibility to prove the retail value of a particular prize rests with the Committee in charge of the competition.
Note 2: It is recommended that the total value of prizes in a gross competition, or each division of a handicap competition, should not exceed twice the prescribed limit in an 18-hole competition, three times in a 36-hole competition, five times in a 54-hole competition and six times in a 72-hole competition.
While I agree that Am's play for money all the time. The USGA does not condon it.