The various Armani lines are sold only at exclusive Armani boutiques or some expensive department stores in your area.
Be familiar with the various label colors such as Giorgio Armani Black Label clothes' labels have white lettering on black labels; Giorgio Armani Classico labels have silver letters with backgrounds being navy blue and for Giorgio Armani Collezioni labels there will be black letters on white labels.
The name of Armani on all the labels will be written in Capital or Upper Case letters which is a very common identification of original Armani stuff.
As you will hold the Armani cloth in your hand, the stuff will speak itself whether it is original or not. The high quality of the clothing stuff can be easily recognized.
Give a closer look at the stitching. If it is uneven or somewhat loose with some clustering or wrinkling along the seams then it is fake.
If the design of the cloth given an untidy look it is not original as the real Armani stuff has some classically featured lining.
Visit Armani clothing websites to have a knowhow of original Armani look. Compare the photos with Armani clothes for sale and do not buy if the photos do not match with the clothes for sale.
Verify the Logo dispatched to the product, compare that logo with the original Armani logo
You can ask the seller to provide you proof for the original Armani stuff and there is no need to buy if the seller does not satisfy your query.