Lack of creativity and interest in the marketplace. If you're an avid nerd, you roughly know what your junk is worth. If you're just some average dude, maybe you bought that pedal last year for $150 and never clicked with it and you don't have a clue what it's worth. When Reverb tells you $125 is fair, you think, "Wow, that pedal must be popular!" and you take their advice.