I can't imagine a reputable site like Luckyscent/Scent Bar selling a fake. I have purchased from them numerous times, and they maintain a near perfect reputation and are well respected.
I can understand your concerns with the cap being loose, but I recently purchased a large bottle of Royal Oud full retail from Neiman Marcus and the cap comes off very easily. My cap sounds just like yours, but I know it's legit and am otherwise very happy. Also, I am fairly certain that the smaller bottles of GIT are clear, but don't take my word on it because I have one of the larger black bottles.
How does the actual fragrance smell? If it smells legit, then it is legit. Your nose is the best way to tell.