Hypothetical Math to Calculate Trading Volume using EchoMTG
Trading Volume Example: Siege Rhino
Right now we know 170 register Echo players own 568 Siege Rhinos; ~3.5 for each player. This total accounts for a volume of Siege Rhinos on tracked on Echo at $2,385.60USD. 170 players account for 8.5% of the total player base on EchoMTG. In 2013, there was an estimated 12 Million magic players (source). 1,020,000 is 8.5% of 12 million, which averaging 3.5 Siege Rhinos a piece, accounts for 3,750,000 Siege Rhinos printed in circulation. That roughly puts Siege Rhino's total volume at 15 Million USD.
Calculating total Secondary Market Volume
Siege Rhino is a single card in a secondary market with 25,000+ different card printings in it. Right now we know there are 1428 cards with a current price greater than $4USD, ranging anywhere from $4USD to $10,000USD each. For the sake of brains, lets assume they all have a similar volume. Doing so puts the secondary market at $21.4 Billion Dollars. Want to try to buy out Siege Rhino now?
I'm just a programmer making wild assumptions here, but one thing is clear, the secondary market is a real thing that drives many LGS storefronts, online sales, and new product opening. Even if that number of off by 50% in either direction, the number is still staggering. To put it in context, if these assumptions are near to the truth, than the secondary market for magic cards is larger than the Electronic & Computer Repair Services market (source).
If you have suggestions to help make this math clearer or more accurate, please comment below.