If I really liked the mare I'd want to know if she was just a grumpy mare, or if she was trying to tell me something, so I would get her vetted if I was intending to purchase...£300 or so is very little compared to long term veterinary attention
My mare is grumpy to do up the front of her rug up and when I put her saddle on. There is no reason for it. I'm just careful she doesn't bite me and am very gentle about putting saddle on and doing girth up. When doing front of rug up I pull it right forward, do it up and pull it back. She's always been like this I guess it must be past experience as she's never had any problems with me .