sentences:  In practice, many items are not in stock, or are not in the same condition, or the price at which the stamp is for sale differs for some other reason from that shown in the catalogue.The Gibbons catalogue was originally published as a penny price list in November 1865.Unlike some other markets, such as stocks and shares, the majority of transactions in the philatelic or stamp market take place informally, by mail order or in retail environments, and therefore the size of the market is difficult to determine.