When I buy off ebay, I look for a fragrance that has a seal and a box. Also, I look for sellers with at least 99.5% approval rating. If the approval rating is lower than 99.5% then I read the comments/complaints to make a determination about the reliability of the seller. If the bottle has been opened, I email the seller and ask if the contents smell "good" (a subjective question, I realize). Many sellers will include information about the conditions under which the bottle has been stored and I hope to see that it has been stored in a dark, cool, dry, smoke-free environment. Using these criteria, I have been satisfied with my purchases. Good luck!