sometimes the best horses are the ones with a 'slight' problem. if you like this mare and are prepaired to look after this problem then i would get her. one of my previous horses had to be sedated for alot of stuff but i loved her and had she was the best buy ive ever got!
i think that despite this problem, your the one whos going to be riding her and looking after her and if it doesnt effect her, go for it.
if you really really want her and if this problem doesn't ultimately affect her performance and you can still do what you want with her could you perhaps negotiate/haggle on selling price.
If you are worried about insurance then I would ring up the insurance company you are thinking of going with and asking what limitations they would put on the insurance.
go with your gut, as others have said she could have got this any time, the only problem will be the insurance. It might be an idea if the owners have her insured to ask them to investigate so it is covered on their insurance then you can make the decision.
One of my horses makes a slight noise, he whistles and his right side of larynx is paralysed, (95% of cases is the Left - so he really is special)
I would advise this horse cantered - and monitored
and if fit enough
galloped and monitored. - Mine hunts all day and gets ** fit and still absorbs maximum oxygen even with this issue.
Naturally you can use it to your advantage £$£$ wise if they hadnt told you about it before hand
What do you want to use him for? Incidently mine can turn his whistle on and off - when he is nervous or frightened - he can whistle too.
If a roarer I would speak to your vet seriously as this is a much bigger rattle.
Personally I wouldn't, I'd rather purchase a horse without a wind problem, even if it is minor, but that's just me...and you did ask, if I was dead set on the horse I'd want a second opinion and looking at more closely.
You have gone to the lengths of having a vetting to pick these things up, therefore your taking gamble after the vet has found the fault, if could be ok and never effect the mare then again it could become worse as time goes on and may only be able to do light work.