You can get red ones through veteran rewards. If you have paid for your account for 12 months you will qualify to claim one. Unlike the original full soulstones (blue and green), these red ones do not come in a token form, but you receive the actual soulstone right away instead. It is account bound (tradeable, but worthless because no one else can use it). These are genuine full soulstones as far as end-user functionality, with unlimited uses (maximum one use per 24 hours). Once claimed, they only differ in color from the blue or green oldschool versons.
When someone is selling an orginal blue or green full soulstone, it must be a round token that says 'your soulstone'... worth a few million. (Can also be purchased from EA for dollars at uogamecodes.com)
When someone is selling a soulstone fragment, it must be a round token that says 'your soulstone fragment' on it. These, when claimed, will give you five uses. They sell for only a few hundred thousand.
As mentioned, always buy soulstones in token form, they are useless to you otherwise (except for decor).