(a) For purposes of these regulations, the term commodity shall not include stamps or numismatic coins whose fair market value is at least 20 percent higher than the value of the metal they contain, where such numismatic coins or stamps are sold by any person or firm whose income from the sale of such numismatic coins or stamps derives substantially from retail sales in face-to-face transactions with purchasers in retail stores.

(b) The term substantially shall mean 75 percent or more of such income.

(c) The term person shall mean an individual, firm, company, partnership, corporation, trust or association.