If I knew the horse/had a good idea on why, then yes. If not Id walk away. Purely because Ive found in the past when sellers say a harmless buck or rear, they mean vertical belly showing to get you off.
I dont know how my partner copes with my inability to not babble, ability to over analyse everything and temper tantrums! He poo picks, loves the horses as much as I do and yet was not horsey before meeting me.
Currently also having to provide a leg up everytime I ride and has to sit around...