It's no longer your gear, it belongs to them. They can put a price of $1,000,000 on it or take it out in a field and burn it, not your business or concern. Yet, somehow you feel since they made a tidy profit selling it they somehow 'owe' you something if you do business with them again. Pretty silly to expect that.
This is exactly right.
This ain't rocket science.
1. Go to hifishark and use the filters for where you're selling; search your gear.
2. Look at current prices paid for your gear and look at recent "Expired" sales. Set outliers aside (fire sales) and average the other numbers. That's what you *might* get on the open market.
3. Look at TMR's offer. It will be lower. Often much lower. Sit with the difference and then make a choice.
4. Don't look back.
It ain't hard.

