@
riccardo,
This key, if when input phone activation vanishes and you get a notification that the key is expired, what you have is a blacklisted product key. The installation and product key on this laptop are either *very* unlucky to have been leaked, or this particular installation is not legitimate. There are no other explanations for that behavior, as that is the way the software is designed to behave when you enter a key that has "expired" (aka, no longer available for use due to piracy).
Note that the former is not possible, leaving only the latter option, and here's why:
First, the key on those stickers aren't done in ink that would have gotten smudged in that way, as the writing is embedded inside layers of the sticker (amongst other things).
Second, no OEM (royalty or retail) is allowed to put a static activation key on an OEM sticker, because all of those are randomly generated and unique, just like retail keys. Static SLIC keys are only allowed inside the image - the fact one is on the outside of a key is suspicious (OK, it's more than that).
Lastly, that sticker doesn't even look like an OEM CoA. To wit, Acer should have had specific writing on that sticker, in specific locations, given it's an Acer laptop and an OEM CoA by the coloring and location of the Microsoft logo. From your picture, I see no indication (smudged or otherwise) that the word "Acer" and "OEM" are anywhere on that sticker, either above or below the bar code (which is where it would be if it's not below the "Microsoft" logo to the right). Also, you're missing a second bar code near the top (I don't see any indication one was there, either). Those are standard on all OEM CoA stickers other than Win7 Professional (which is instead a sticker of bluish color with a lot of the UI elements moved around, although all of the text is the same), and what I see here looks quite good, but still fake.
Given what you've got there, it doesn't pass the "smell" test. That user is probably very unlucky, but it appears that Windows 7 license is not genuine.