The most important thing when buying a luxury bag is to buy from a trusted source. Always look for reviews of the seller when you are buying. Buying from a good seller is the best way to get an authentic bag. However, many people will buy used bags in an attempt to save money. In this case, you need to know the bags and the designers. Learn about the styles and the hardware used. Look for the labels on the inside of the bag. Always look at these things before buying. You can buy used bags online, but you have to be very careful if you do this.