Saddle???

Question
I am considering buying a pony for My daughter...he is based at our riding school. My daughter has riden him numerous times and he rides lovely until she puts him into canter where as he will start to buck. He has a leather saddle that previously belonged to another pony that has now left the establishment. The saddle to me doesnt seem like it fits its loose at the shoulders and at the back and I can get My hand almost right underneath it. When she finishes the ride and we remove the saddle even though he is hot and a  bit sweaty there is dry sticky patches on his coat (these are not there when we first put the saddle on). Someone at the riding school has told us that when he first came he had a different saddle and didnt buck at all so do you think this could be the cause of the problem.
I have spoken to the owner regarding the saddle but was told there was nothing wrong with it...and it will do and the pony was just no good. Hes absolutely lovely with a lovely temperment and always does as hes asked apart from the canter. Grateful for any info you could give me.
Sorry if this question seems a bit silly but although my children have been riding for years this will be our first horse.

Answer
Fiona,

Buy the pony and get a saddle that fits him.  The dry patches are where the saddle is too narrow and tight. They come from pressure sufficient to generate heat that will dry the skin and the sweat.  The owner is an inconsiderate idiot and doesn't deserve the pony or any other animal with that sort of attitude.

Lyn