One problem you may be having is that due to the way RTI is sold through a dealer network you are limiting your market to RTI dealers and consumers who some how have obtained a copy of software. (This is a moot point since RTI is moving to a new cloud based licensed platform called APEX very shortly). That being said, no dealer would buy this to sell used, so they would use it a testing platform or in their own home. RTI has dealer based incentives to help dealers obtain product through different programs for this reason. To make it tougher, RTI has introduced the XP-8s which is the same product with more horsepower. Android licenses are less common than IOS as well. Last, being such as important piece of the control system and fairly expensive makes a tough sell for any product.

Your market price is definitely fair, it's just the market that you are dealing with. If I were you I would lower your price from $100 - $150 and you may get some interest. Again, I would not hesitate to purchase this product from you for my own purposes if I didn't have something in place already. I have two XP-8's as well that I am not even going to bother listing.