Some demo,s are as new and hardly used, others are flogged out and very untidy for their age. Ideally you should have a look at the kite first before parting with your cash.
I would also make sure not an ex-school kite.

Agree with Steve.
Ex school kites have a really bad rap but its all in the inspection. Most of ours are hardly used, undamaged and make really great buying.
Consider:
How many days a legit school operates - way less than available kiting days.
How many hrs the school kite is actually flown - way less than a session rider.
What kites are used. Instructors almost always select a kite undersized for the conditions so rarely is a school kite flown in overpowered conditions when wear & tear is at the max.
We have school kites that have gone through a full season with original 'P' lines that arent even flattened let alone worn.
As long as you have the opportunity to check the kite chances are a school kite will be a very good deal.
And they are almost always current models!! Bargain hunters dream.