the appearance of the bottle should give away a bit, first and foremost. secondly, the fragrance. but if it matches the original and you're happy, go for it.
testers are given free of cost to shopkeepers in countries other than Pakistan in order to get consumer feedback. here, everything comes with a price tag so even these little 'businessmen' rob you by selling those. they are supposed to be original, just not for sale. in other words, you can say they are concept/replica cars for sale.