With any of the very expensive oils (any oil for that matter, but it’s worse with the expensive ones) if you find something well below market price you need to ask yourself why. The most likely answer is that it’s either:
1) an out and out fake (an accord made up with synthetics - nothing wrong with those per se - but if you want one of those you can buy one from Perfumer’s Apprentice at a realistic price for what it is) or
2) the real thing but adulterated with something else - the something else could be anything from jojoba oil to DPG, to an accord or just a single synthetic. It could even be another natural oil - rose otto is often cut with geranium oil.
Only buy at below market price if you are convinced that the reason it’s cheap isn’t one of the above. In general, as with most things in life, you get what you pay for.