It can be very tempting when you come across a listing for 10 Ralph Lauren shirts for $120. They look authentic, but how can you be sure? While there is not 100% iron-clad assurance, there are some standard rules you should apply to all such listings. First, if it does not explicited state: guaranteed authentic (designer's name) - then you may want to look elsewhere. Also, look for subtle play on word phrases or suspect use of punctuation. For example if a listing reads: Authentic "Ralph Lauren" polo shirt. The seller may argue that the reason "Ralph Lauren" was in quotes was merely as a means to reference the style of shirt and that it did not mean to imply it was the actual brand. Also, be leary if there is no money back guarantee -that's a red flag. And finally consider feedback - but do not place too much faith in it. Why? Becuse some buyers will not know, realize, or care that what they are buying is a fake. When you read the feedback, look for signs that buyers needed to exchange the item because it did not fit properly. If this is a common theme or occurance it's a pretty good bet the merchandise is fake. As you might imagine, a number of manufacturers can produce a shirt that looks almost, if not completely, identical to the designer brand. Where you will notice the difference is in the fit and the quality of the materials. Often fake shirts run smaller than the authentics. A seller may state that a particular run of the merchandise was produced smaller by the manufacturer..for one reason or another...but keep in mind that Desingers DO NOT vary the size of their shirts. For example, if you went out today to the mall and bought a XL Ralph Lauren Blake shirt it was produced to meet the same exact measurements and percise specifications as the one you may have bought five years ago. Designers are very aware that consumers expect this level of consistency. So if you purchase an item on ebay and it looks authentic, but doesn't fit like other similar items from the same designer you have in your wardrobe, it is likely a fake. In the end, there are probably a number of ebay sellers that feature legitimate authentic designer clothing, but there are also a number that are selling fake or replica items. In my opinion, the only way you, as the consumer, can be sure is to choose to purchase you clothes from a reputable department store (often they have good sales as they mark-down clothing between seasons) or shop at one of several well-known, national discount / close-out/ slight imperfection clothing stores.