One sure test to check whether an item that has been sold as " New" is really new...is to look at the inside seams...when items have been used there is usually some sign of "bobbling" on these seams. Another good check, if there are pockets, is to turn them inside out to look for telltale fluff etc. Pockets also show useage on the seams. Necklines are another place to check for wear and also on the inside of cuffs.
Discoloured labels are NOT a giveaway, as some clothes, especially jeans, are deliberately washed / distressed by the manufacturers.