Hi!
One of our module (http://addons.prestashop.com/en/6270-credit-card-offline-payment-manual-processing.html) has been plagiarized in Addons by Best-Kit.
We came across with this module: http://addons.prestashop.com/en/19409-credit-card-offline-payment-pos-point-of-sales.html. A module with more than 100 fraud sales.
We contacted PrestaShop Legal team to know which actions to take and their first answer was to contact developers. We did it and the developers' response was that the module was done from scratch and that they didn't know anything about the other module. So we contacted again PrestaShop with the evidences.
Check the similarities in the module configuration:
1. They have even decided to use the same image with our information 
And, what a coincidence, they use exactly the same strings. I suppose that this is normal when 2 developers develop 2 modules from scratch
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2. What's more, both of us use the same JS function to toggle a div (and it was not extracted from StackOverflow) And they think that using the same DIVS name was a good idea.
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3. They had also thought about using an object called "card" in every input to store the data, great!
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4. And what about the card form? Does it look similar? It has the same buttons and the same message.
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So after PrestaShop checked it for 3 months, they have decided that there are only similarities in the product page, not in the code, so they have asked them to modify it.
Of course that the problem is not that other company has developed a similar module with the same functionalities than our, but they have used our module with slight differences and Addons allowed it.
So If they consider that this is not illegal, I suppose you can download any Addons module, rename some variables and sell it again as yours, so take profit from the works of other 
I leave here my evidences so that each one can draw its own conclusions.
PD: Apologies for the possible English mistakes
