Trade ins are always low unless there is a subsidy from the mower maker for the dealer to take your old mower & destroy it.
The dealer has to prepare the mower for resale which may include a lot of time and parts then sell it at a profit .
I no longer sell used mowers because there is no profit in it for me .
Buy one privately & it blows up the second the new owner gets it off their trailer and it is tough luck
buy one from a dealer and it faulters 3 months latter & you expect a free warranty service.
In my area I would be offering a maximum trade-in of $400 if it’s in good condition and you’re not a regular customer. If I know you and the unit it would be about $700. You may say I’m ripping you off, but have been burnt to many times ending up with units that aren’t worth reselling. Just hurts my reputation, and would rather lose a sale than my reputation.