It sounds a little good to be true. In fact, incredible if he is an experienced and able 3rd Level horse.
Now, if ther horse is a lovely mover and sound, he may well be worth $3000. Or more, regardless.
But some people say "3rd Level" because the horse performs one or two 3rd Level movements...badly.
Find out if the horse has shown, and when or where, and what the scores were. Do so politely, because again, the horse may absolutely be worth the price and you don't want to insult the owner.
But know what you are buying - it may be a really nice horse that's only ever schooled dressage at home, and the owner thinks his schooling is roughly equal to 3rd Level. And that's fine, and it may be a great horse for you. I just wouldn't want you to expect a schoolmaster or a horse with a competition record and to be disappointed when he's not.
Do post pics and video!