Warning

Sellers who consistently sell itunes vouchers/gift cards for less than face value quickly (6+ mos) go out of business, many times because they can't keep up the honest (no more credit) or dishonest (got arrested) way of getting the vouchers.   Sure you probably knew that, but did you know the dishonest methods a seller uses for procuring itunes vouchers can adversely effect you too? 

If someone uses a stolen credit card  to purchase itunes vouchers Apple has the ability to shut down the code prior to use, moreover, Apple also reserves the right to take back     'credit(s)' that were already used on accounts that they find were funded with improperly purchased vouchers/gift cards.   Yes, that means you could actually buy codes, use them, then much later on get notification from Apple that you have a negative balance.

If your 'discount' seller cannot, or will not, show you (a picture) of the physical card

 and the corresponding receipt, with matching serial numbers, find another seller.

Why take the chance?

Apple only allows stores with massively high volume to be 'authorized distributors' therefore essentially all of the ligitimate cards sold on ebay were purchased at face value from a retail store; as you may know, Ebay and Paypal charge a combined fee equal to about 6% of the sale price, so it stands to reason that selling codes at less than face value is a short lived venture (beit honest or not).

Avoid trouble by finding a stable and reliable vendor.  Select a seller who actually appears to specialize in itunes sales, as indicated more by their sales history and current inventory than by their username.  A Power Seller with over a year's experience in selling itunes and over 95%+ positive feedback is clearly a proven producer you SHOULD be able to rely, but remember no one is perfect.

If you have specific concern (about itunes vouchers) that you believe would be of great interest to the ebay community please send me a message and I will address it publicly.