From my perspective the price depends on a number of things, including but not limited to: how old it is, how much has it been used (or shows signs of use), is it faded, are there any patches, any damage, any mold/mildew inside, how are the valves, etc? Is the seller and outfitter or a private party? Keep in mind that as a general rule of thumb the retail price of inflatables goes up around 5%-8% a year. Just because it retails for $1,600 today doesn't mean it's worth $900 used. Depending on how old it is and now it was bought (pro-deal or retail) the seller may have only paid $900 or less to begin with.