I brought one from her and know others who have done so, also sold one on through her. (She's very local to me.) I'd say just do the normal things you would when buying any other horse i.e vetting, get someone else to look at it etc. She was a nice lady and I tried the horse a few times before I made the decision and she was helpful with getting tack etc.
Cattie - thanks for that, I met her and found her a lovely person and so so knowledgeable (she even gave me a bit of advice when I was riding the pony about my postion etc and what I needed to do when trying the pony out)