[Catalysteffect]

So i've been going into walmarts and taking blank cards and then bringing them home and using a hairdryer to peel off the sticker on the back. But i've noticed a lot of them producing nothing at all. I've been wondering why that is when some in the batch I drop off get a balance at some point but then their is a lot that don't. So is me using the hair dryer to melt the glue wrecking the card in some way. I even went to the lengths of returning something to get a gift card and they would use the card i planted. So when they went to use it, their system crashed. They had to manually enter it in. So what I'm doing has to be doing something to these cards. So if this the case how can get the sticker off without wrecking the card. Just using a exacto knife is hit or mis and it still messes up the sticker in a way. Using the hair dryer makes it easier and makes it looked not tampered with.