Is he registered, and do they have the original papers?
Who are his mother and father?
What is their lineage?
What condition is he in?
Does he have any special needs/health problems?
What is his personality like? Is he easy going, 'spirited', lazy, ect.
How tall is he?
What kind of training does the horse have, if any?
Who trained it?
What is the horse's background? What has it been doing?
Does it have any vices?
Does he load and trailer, stand tied, and behave when you bathe him?
Has he had any injuries in the past?
Has he been kept in a stall or pasture?
Does he get along well with other horses/animals?
Does he have a current coggins test? If not, will you get him tested if I buy him?
Has he been vet checked? If not, will you pay a vet to check him if I like him?
Are his vaccines up to date?
Do you have a record of all health care?
Any treatments done for worms?
Are the teeth in good condition, have there been any treatments for them?
Has he had any problems with his legs or hooves?
Any problems with muscles or colic?
Is he eating well and with a good appetite?
Good luck and have fun with that filly! : D

An 11 month old horse should be given a vaccine for worms to prevent diseases. Their health care should be well monitored just like any other animal and you may visit a vet to learn how to take care of it.

Well you should see if a vet or a experienced horse personal can come with you