A very well known way of cheating the Steam system and unlocking achievements is to use the
Steam Achievement Manager, also known as SAM. This tool is compatible with any Steam game which has achievements in it, and is handy for many things including bragging to your friends or unlocking achievement based weapons and items.
Click on that link which I provided, install the tool and choose your cheeves. For more information, read the shit on the site.
Have fun, and I accept no responsibility if you get VAC banned after using this tool.
Comments
No one I know personally has been banned using this tool. I've used it before to unlock some items, and I haven't been banned. My friend has used it religiously for ages and hasn't been banned.
The site states that it is improbable that you'll get banned, so I'd say you're pretty safe.