As with most things it's a matter of finding the right buyer with regards to what it's worth. I sold my Insight+ back in '23-'24, after about 6 months in the Trading Post, and price reductions, for $150. That was after having purchased a new DAC 5 in 2019, and having more DACs than needed. At that time $350 was what I figured it was worth as well based on the limited sale info available on the net. It's only drawback in today's market is the single coax input. It's definitely a good sounding unit, though I like my AVA Ultra DAC a bit more, which I kept for backup.
Their brokerage service is a good way to go as the buyer will receive the 1 yr warranty on the unit. Mary will be fair in advising what they think they can get for your piece, you just need to be patient for the right pair of eyes to see it. GLWS