Trade vs. CarMax vs. Carvana

Tesla offered us an amount for a trade of $29,500. We declined the offer and are still deciding whether we want to keep the Volvo or sell it. But we checked with Carvana, who has given a sight-unseen offer of $33,000. So we checked CarMax, who offered $30,000. Seems like a fair difference between Carvana and the others.

Has anyone on here had any experience selling to Carvana? Do they do this and then drop their offer later? Or is it legitimate?

thanks,
Kevin