This specific auction looks good to me, but Lacoste, Boss, Mugler and so on is tricky on eBay. I personally would only buy, if the seller can guarantee the authenticity via e-mail. The fact that it's a tester is a good sign, fake bottles normally come in the original packaging. But you can't always trust the photo. Often sellers shoot a pic of the original and sell the fake one. The sellers feedback is 100% at the moment. Another indication for trustable eBayer.