One of the problems is "pickers." Pickers usually don't have much general knowledge, meaning a little knowledge about a lot of categories. Unless you know something about guitars it is difficult to spot a good one, where petroliana comes in bright colors and is easy to identify.

Jack Sim

Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at www.gaspumpbible.com
Air Meter ID book also available