Creating NFTs for free seems too good to be true: what is the catch?

So, I'm not into NFTs but I understand the basic concepts. While looking for more infos online I found a website proposing to host NFTs for "free": that means minting the NFT only when sold, so that you don't have to advance money for its creation. I feel there must be a scam somewhere: there's no way it's that easy to make money! I would be glad if someone with more knowledge or experience explained me