Similar to Gambling scam already mentioned in the sticky but people also have to beware of Russians adding random in the Steam official OPSKINS community group, they add you with the intention for some gambling deal that they are a moderator or admin of a gambling site and want to make you win skins in exchange for 30% of your skins won. Avoid at all costs, once you deposit those skins they are gone.
Don't fall for it as I was attempted to be scammed by one. Currently the dick is is banned on steamrep.
His profile name is Harley TRADE DOPLER GAMA on steam.