If you’re already in game and the user is offering them through gifts or trade, and you don’t have to give anything in return, then this is fine. You may receive their gift.

However, if they’re offering free pets on social media, this is very likely a form of bait. In many cases, the individual will send a link for you to join them through, or ask you to do tasks that give them your information in order for you to get pets that don’t really exist. You should block them and report them immediately.