...I fear people might start listing modules at unrealistic prices in order to game such a guide. Both inflated and undervalued scenarios are plausible.
-- senor-bling
Actually, a problem like this exists on eBay, and he's known as the "Flower Pot Guy". Infamous. The user posts up pro audio gear at prices which are sometimes twice the normal average, and charges "normal" prices for stuff that's broken. The name comes from his habit of putting the gear in front of some cheap clay flowerpots before photographing it, and its been going on for literally years.
The problem arises when you have non-online dealers that might be trying to price some obscure device, and they use this bastard's inflated prices as their own, because...hey, HE asked that, so WE should ask that too! I've actually run into this once or twice, and dissuading dealers from following this jackass's prices is like pulling teeth...until/unless they recognize that they might not sell the device in question at those insane prices of his. But his antics have caused considerable problems on that platform for pro audio shoppers for the precise reason you mention here. MOST...but not all...have learned to ignore him, but his "au-thor-i-tay" is still occasionally cited by non-eBayers for their own psychotic used gear prices.