Well said and correct. The market will find a way to place a value on items that you want to buy or sell (whether you think it's fair it or not). :-)
Most used items will net you 30% to 50% of retail. Some less than 30% and not many more than 50%.
That is the item value lost by the enjoyment gained from being the first person to open the box.
I have used TMR many times both to buy and sell.
If they give you a cash offer the amount will make sure they can end up with a profit for the sale. For very new gear this might be the best choice.
Also as stated above you can consign to them and you will (possibly) get a little more money for your gear.
I have actually done better just consigning to them but as stated you will have to be patient and not need the money right away.
I give them 10 out of 10 for everything they do and how professional every aspect of the selling process is handled.