I got mine used, but used for a week. I got mine on the B&S forum. It was tested for infinity, and it is 100% accurate. If you buy from Adorama, Amazon or B&H, it's all good.
bought my Rokinon 14mm from Adorama new - one test shot and I knew I had a winner. Same with my 85mm f1.4 Rokinon which I bought used on ebay - perfect lens.
Although slightly off the topic. Both these Rokinon lenses the 14 and the 8 are really nice optics for the price. I have the 14-24 Nikkor so I dumped the 14. But I've held onto the 8 for use on my DX bodies and having used the 10.5 Nikkor, I had to say I like the 8 Rokinon better.. It's just IMO.
Just for those that MAY be wondering about the line as a whole.
I found a used Rokinon 14/2.8 finally. Here's one of my first shots with it. I'm still getting used to accurately focusing the lens but, so far I think this is going to be a great addition.
D800, 1/50th sec, f5.6 or f8 (can't remember), iso1600 Exit by mkrepp, on Flickr
- they are all the same except for name. There are two versions. I have the newest one (confirmation chip in it). 
