I'm not an Argie collector for just this reason, but frankly, i'm also a bit of a risk taker when it comes to playing what i cal "Pony Roulette" True, the house wins quite a few times, but i've scored some pretty amazing AND genuine variants by taking the leap of faith!
A big part of Pony Roulette is going with your true gut, though, and not your head or heart. However, if you truly like the way she looks and she isn't too dauntingly expensive, go ahead and get her! If you're looking for an original pony as an investment to sell down the line and make money off of, though, that's when you just need to trust your instinct. Ask for as much info as you can get...where was it found, a pic of the inside of the head and backside, and go from there.
Good luck!!