Is the item well constructed? Loose threads, crooked stitching, inconsistent colors or mismatched patterns are telltale signs of a fake or knock-off.
Is the price too good to be true? If the real item can command a certain price, why would the designer or manufacturer ever have to resort to discounts?
If the item is made of leather, is the leather supple and smooth with no flaws? Does it smell like genuine leather?
Do zippers glide smoothly?
Are the words on the label spelled correctly? Is the logo correct?