Depends on what you mean by slightly used. You can get a new one with nearly identical specs for 1399.
MSI GT70 Dominator-894 17.3" Gaming GT70 DOMINATOR-894 B&H
Processor is slightly lower spec but very slightly, not noticeable most likely:
Intel Core i7 4810MQ vs 4800MQ
Do you get any remaining warranty on the used on transferred to you (it may be device bound and not person bound)?
It's not a bad price, but not a great one either. You'll save 100-200 bucks after tax but you need to double check the warranty and you don't know where that thing's been, could have spilled diet coke on it or something and is trying to offload it. Depends on how much you trust the seller and how lightly used it really is.
It'd be a good deal at around $1-1.1k