If you ARE serious about buying the horse, do make sure you watch the owner ride her in all paces, and you ride her in all paces. It is very, very easy for dishonesty to sneak into the deal, no matter how sweet the horse may seem at the moment or what the owner tells you. Dougal got sold to us as a green but safe, quiet pony that had never bucked/reared/bolted/napped and what do you know, he's done all those things. My mother made the mistake of not seeing him being cantered [or cantering him herself], not knowing that he bucks a lot when asked to canter. Even little things like that can catch you out.
Anyway, enough rambling. Just be very careful, it's easy to fall in love with a horse and ignore any sneaking suspicions that don't seem quite right. Good luck, i'm sure you will make the right decision at the end of the day.