what is this black patch on the back side of the wifi card

I recently bought this dw1830 over ebay. The card works but I'm wondering what is this black patch on the back side. The seller said its used item removed from another laptop but do you think it's some bad/quick fixing hidden behind the patch. I've not tried removing the patch because otherwise the card is working but I'm thinking of quick/dirty fixing which might reveal after some use.
Do you think I should take this up with the seller?

I'm saying this because something similar happened...

what is this black patch on the back side of the wifi card