Don’t buy from them. They don’t seem vetted.

Here are alternative known good sellers that also offer great discounts:

• Humble Bundle
• Green Man Gaming
• Fanatical
• Game Billet

There are others that are legitimate.

Avoid places like the site you listed, and also these ones especially:

• G2A
• Kinguin

If you buy from Eneba, G2A, Kinguin, etc. you may be fine. However, there’s risk that you may not be fine and have a key that was purchased via a scam or stolen credit card. Then that game which is linked to you can be deactivated from your Steam account, possible Steam account ban, etc. Don’t buy from them because you just don’t know where that key may have come from.