If you are already in the game and the user is offering them through gifts or trade, and you don’t have to give anything in return, this is fine. You may receive their gift.
However, if they’re offering free pets on social media, this is likely bait. In many cases, the individual will send a link for you to join them or ask you to do tasks that give them your information for you to get pets that don’t exist. You should block them and report them to the social media platform and/or Roblox immediately.