I actually don't like full Arabs. I have two part-breds and they are brilliant horses but I'm not into the pures.
I looked back at your first post and at 18 months her faults may correct, but I have seen much nicer full Arabs that are her age sell for much less (I have a friend whose mother just got out of breeding them because of a series of disasters).
I'm in Australia though, not even the same country as you, so our horse market is very different. In a strong market it isn't possible to get quality, registered youngstock for less than $5000. In the current market there are numerous VERY nice yearlings and two-year-olds for sale for $1000 and even less - as I said that's what I paid for my yearling and she is LOVELY, but unregistered, and I don't know if she can be.
If you want a full Arab, then don't buy one without papers, because there's no guarantee. If you want a horse that looks like an Arab, then papers don't matter. The most "Arab type" horse I ever saw was only 25% Arab.
This particular filly is VERY Araby in the face and croup, not so much in the ears (my filly is more Araby in the ears than that and I don't know her percentage). I wouldn't put it past a seller (any seller, including someone who you trust) to be lying and in this case, her supposed blood status could be the truth or a lie. I have seen full Arabs that were less typey than her, and part Arabs more typey.
There are people on here who are very much into the pure Arabs and who will be able to tell you more. I only have partbreds and what I know is what I've learned from my friend whose mother used to breed them - and that's only one strain (Crabbet Arabs). That one strain, by the way, is the only strain of purebred Arabs I like. They have substance to them, unlike the finer "showring" type Egyptian lines.