The link looks like a gray market import from China. You might get slapped with import tax, and you might have trouble claiming warranty. As Tamron has poor quality control, your lens might come with AF calibration issues or other problems, in which case you need to use that warranty. Also, the rating of this shop is not as high as it should be. You really want a seller 99.9% or higher rating. I would beware.
My strategy is to look at the seller rating (preferably 100% positive) and then I try to find out why the seller is selling this lens. I'd rather buy a used lens from a highly rated guy that is switching systems, than a new lens from a dodgy shop or seller.
I've bought most of my lenses used on eBay, and always from people switching systems. I've always gotten excellent copies.