If you will not check the username and let the twitter name plus others comments of getting the Free ETH be the basis, you will be deceived for sure. Yobit tweeted[1] about that though. Also, come to think of it ~ if it's from the real Yobit, why wouldn't they make a tweet about it, I mean, why post it in the comments instead.
AFAIK, account owners couldn't delete the comments directly, but they can block and report the account. However, I don't think Yobit would bother doing that. The giveaway comments might be automated, not sure, but I think hackers are using bots to do that for them.
Just don't send money to receive a free money, if it's really free, you don't need to pay to get it.
[1]
Many fake msgs in Twitter about "giving away ETH" from fake accounts, don't pay to these scammers