It's a shame and I'd feel really pissed if I were you. But you tried your best to sell it under your own terms and for whatever reason, it didn't happen for you.
I sold my last car (59 plate Jaguar XF) through a company who contacted me after I placed an advert in Autotrader. I waited until the advert ran out and had to decide whether to readvertise or accept a price which was probably £1,000 under the recommended value. I settled for the lesser price as it suited me and meant I could get on with my life.
Of course, when the phone rings and a potential buyer asks if it's still available before its actually been collected by the company it feels a bit like a kick in the happy sacks. But you quickly get over it. Don't look back!