Ebay is full of fake Diesel Zaf 796 wash, i reckon at least 95% of the listings are fakes and i personally have purchased fake ones from ebay after not asking for more information or believing the sellers descriptions.
First thing to look for is the photo the seller is using, is it a picture of the actual jeans or does it look like a stock photo? If it's a stock photo then i can almost guarantee they are selling fakes - if it is then ask for photos of the actual jeans and if they cannot produce them then ask yourself why not? What are they trying to hide. There's currently a seller listing loads of Zaf's all with a stock photo, i have asked for pictures of the actual jeans and heard nothing. Ignore the high feedback and don't be drawn into thinking you've got a bargain because you wont have - you pay for what you get remember! Don't be fooled - ask for the photos of the back pockets and micro-stitching.
I see people paying between £20-£50 for fake Zaf's at the moment!! Diesels are expensive and quality jeans, look at the Zaf's for sale at £80-£90 and compare the pictures, you'll spot the quality difference.
Obvious signs that they are fakes (that's if you get to see the actual jeans);
1) Look at the back pockets - where the darker denim meets the lighter denim that shape 'dips' slightly before going up to the point on originals and is more of a true curve. Fakes ive seen just go across then up or 'dip' too much.
2) Look at the colouring, lots of fakes are very streaky on the front of the legs and the rusty affect doesnt look rusty at all and sometimes they're not even rusty. True 796's have a very good rust affect. The distressed patch at the opposite side to the coin pocket should be there too and look like proper distressing as oppose to a few scratches.
3) Check the microstiching on the label (this goes for most diesels).Under the "Made in Italy" there is a little white or silver lining. Look really closely and you will see the letters DIESEL etched in there if the jeans are authentic. Also on a real pair of diesels there are little tiny hard to read numbers above the Indian head on the inside label, you have to look reallyclose but they should be something like77 55-3607.
4) Ignore that the seller says such things as "order one size up" etc. Zaf 796 run true to size, if in doubt ask for the actual measurements.
There's plenty of other checks but take some time to check out sites such as honestforum or honestwiki both of these offer great information on Diesels and will save you buying fakes!!