It's a perosnal choice. Pay $1500 +/- right now direct from Bitmain and wait until late January to get them, or pay 2-3x that now from someome who has one and be mining in 3-5 days. How much is that 1.5 months wait worth it to you? I personally ordered 2 S9 January batch and chose to wait.

PS waiting has not been easy!

Anyone charging more would be shipping from standing stock (or it's a scam). Most manufacturers charging less to sell directly are backordered a couple months.

Supply and demand.  There's a limited supply, and very high demand relatively.  That's the case where a miner costs so much more from say fleabay than direct from the manufacturer.
If a seller is offering a miner at a cost much less than the manufacturer does, that's a scam.