Example (click to enlarge):
The fake above looks like it is made out of an old couch. When buying Dior Homme online, keep the designer's aesthetic in mind. If it looks like a thoughtless 80's Christmas gift you received from your aunt, do you really want it?
Example (click to enlarge):
Speaking of the Dior Homme aesthetic; this beauty has a large gray "CD" logo printed on the front of the tie. In-your-face logos are not the brand's style (the women's line is another story). At first glance this tie looks like it may be an older piece from Christian Dior, circa their creatively-starved 70's and 80's years. However this gem has a fake Dior Homme label on it and was listed as a Dior Homme piece. The lining has a fake version of the "Dior" repeating pattern, with the letters spaced too far apart.
Example (click to enlarge):
The fabric content tags in Dior Homme ties are located in the fold, on the back of the skinny part of the tie. These tags are always silver with black stitched lettering, and the label is sewn folded in half. Above is an example of a fake fabric content tag. There are several things wrong with it. For one thing, the label is a blackish purple or something, not silver. Second, the lettering is too close together and stitched in white. Lastly, it reads "Made in China." Dior does not produce any clothing or accessories in China. To the best of my knowledge, Dior Homme makes all of its ties in Italy.
In the end, ties are one thing I recommend buying direct from the store. They run around $170 (USD) and the authentic ones don't sell for much less on eBay. If you do choose to bid on one remember to ask for detailed photos if none are provided. Also, feel free to ask the seller where he purchased the tie from and if he guarantees authenticity. Keep in mind that the seller's response in no way guarantees authenticity. But, some sellers will try to warn off informed buyers with a line like "It looks authentic but I can't guarantee it," or "I'm selling it for a friend who says it is authentic."