where did you price it at? I would try eBay and it's worth more to get an idea of what you could realistically get. Apple offers $690 for trade in .....I think you could get $150-$200 more than that
I got the price at Cashify (a trusted service in India for selling old gadgets). Seeing the nearly $3,000 price tag for the identical iPad Pro with M5 made me realise the M4 is worth a lot more.