I've been contacted (through Steam profile comments) by a few people in the past month, asking me to add them as a friend.
Examples of comments left on my profile include the following:
> Hey! Can you add me just for a little chat? I couldn't send you friend request...
> yo mate, send me friend request, i've got something for you
I've searched some of these up, and some of these comments (in their exact wording) can be found on other people's Steam profile comments.
I don't believe for a second that they're unable to send a friend request, so I'm inclined to believe that they're all scammers/bots. They all have the default (green-fade-to-black polka dot) profile background, and the same default teal profile theme. Profile pictures appear to be inconsistent.
So my question is, are they all scammers? Is my suspicion correct? Why couldn't they add me, and they need me to add them? Usually scammers just add you first and say something like "It's me your brother" and send you a phishing link. I know there was a thing a while back, where if someone is on your friend's list, and they send you a Steam call, they can grab your IP address. So I'm hesitant to this day, about adding someone to my friend's list.
Hopefully someone with more experience in this subject can enlighten me, and everyone else who searches this subject on Google, for posterity.