So, long story short, a user recently posted that their monero tx went through with a gigantic fee, something they didn't plan on. You can see here:
The user was using a remote node.
As of now, the plausible explanation is that the remote node operator was nefarious. The way the system is currently setup, the monero daemon (the remote node) calculates the fee required to submit a transaction to the network.
So, 1) run your own node. And 2) if you are going to trust other people's nodes, double check the tx fees.
Hopefully there's a way to address this, but it probably won't fly out soon.