I sold my wife's Pedego on Craigslist. There's a lot to be said for selling locally. CL, Offerup are good choices.

As for pricing, if it's a name brand ... look at CL and Ebay (filter for "closed/sold" only). If its not a name brand, use your best guess and be prepared to drop the price if/when it doesn't sell.

Knowledgable buyers will be most concerned about battery health; if you've kept really detailed charging logs that may go a long way to ease their concern(s).