I paid $760 for a transaction yesterday, sending bitcoins using TrustWallet.
This wallet offered me the default commission size, and I was stupid enough not to double-check the information (although I always do this in Electrum and other wallets). At that second I thought that TrustWallet should set the optimal commission according to the mempool, but now I started to think that these bastards are in cahoots with the mining pools since they offer users commissions of crazy size by default.
This was the last day I used TrustWallet

What would the fees have been if you didn't get this wrong? Were it tons of outputs?