Who said anything about a sticker? If a system has a key that can be recovered, it can be resold. Of course, the seller might have to prove to the police that they aren't selling the same key over and over.
Again, wishful thinking. Licence is embedded into bios. There is no serial to recover.
You'll have to take that up with the court in the EU
And EU court said that you can resell retail software. Not resell something that came with hardware like OEM OS separately.
Neither Microsoft, nor the BSA, nor law enforcement has any say in the matter since the keys were legally purchased
Except they were not. If you did not properly obtain a valid licence, you can show your crappy invoices, cry as much as you want, but they will screw you without any lubricant.
all you'd have is an invoice.
On which they will laugh at. Since you purchased some dodgy key, not a valid licence. I looked at several such websites, and none of them even says you
purchase a licence. They say you purchase a key.
Again, I'd rather pirate software all day long rather that bring my money into pockets of criminals. It's not only a copyright issue. It's a credit card an other types of fraud which cause real damage to both innocent people and IP owners. When licences are purchased by stolen credit cards, there are two options. Either card owner lost their money or there was a charge-back and then IP owner lost that money. It's not as simple a giving money back, there are some real monetary losses in the process.