I have seen those deals on Ebay. They might be honest, but who knows? Unless they provide an assay statement along with the silver wire..but even then I don't trust it.
I do trust vendors like Silvergen and Silverpuppy. They are reputable and they sell silver wire. Why take a chance? But here is one other option that you should seriously consider: A Canadian Silver Maple Leaf coin. The purity of the coin is 99.99% silver, also the highest among other bullions which have a 99.90% standard. Two of these coins wired to your CS generator will give you the highest purity silver available, totally trustworthy, and will last a hundred years! You can get them at coin dealers, or off Ebay. I use them for my homebrew CS generators. Its a bit of a pain to use them with the SG6 because it is designed for wire. But if you have a clip lead generator, it shoud be easy enough to figure out. I could just run clip leads from the SG6 to the coins and then suspend them in the distilled water, but then the stirring is a problem because the SG6 uses a top stir motor, not a base magnetic stir. But my homebrew generators use base mag stirrers. You get the picture. The coins are pricey, but they will last longer than most human lives.

The best place I have found for silver, well for that matter the best C generator (in my opinion) is at http://www.health2us.com/. Fred sells a troy ounce of silver with predrilled holes at a very reasonable price. I have used my C maker from him now for over 4 years and have made hundreds and hundreds of gallons of very fine CS. Each batch is perfect and it is made to last.