I agree. I didn't mean to imply that TDA will bust every trade.....But I always have a right to voice a complaint for what I consider a bad fill. Sometimes it works, sometimes not. Sometimes I don't bother.
This is a multi-billion dollar business... And actually that exact market maker is likely the one who spent $1 billion buying cars and houses: https://therealdeal.com/2020/08/27/ken-griffin-is-approaching-1b-in-worldwide-luxury-real-estate/ The stock market is an ocean filled with predatory sharks trying to cheat everyone else out of a dollar, or even a few cents; otherwise they fall prey to someone else doing the same. A few hundred dollars is their grand prize, and some may be doing this thousands of times a day. I've also lost $hundreds on some trades, as well as I've made $hundreds or even $thousands on some option trades that I was able to buy cheap because someone else made a mistake or was in rush of selling. Sometimes the broker busted my trades because the other party complained. I don't get much of mispriced options anymore and prices got fairer for everyone (I think), but even today I was able to buy an AMZN options combo where I seem to have paid $1K cheaper than the "fair" price may be (the profit was showing instantly): Though most of the time we all overpay for options, and over time I've overpaid $10 to $100 on so many option combos that market makers easily made $100K+ off of me. While I don't see a reason why some of the most clever market makers wouldn't be able to scoop some strongly mispriced options when they are the first to spot it (in nanoseconds), or when they already have bids waiting to buy at the lowest price.
ShortVega, Unless you are looking at the time and sales of that butterfly and see trades within seconds on both sides of your trade, you can't say it was "going for $13". the brutal truth is, is that nobody else wanted your trade, so Mr.$5 trader took the opposite side of your trade at $5. I have gotten fills multiple times on vertical spreads for more than the spread was worth, to my advantage. I almost feel sorry for the unlucky person on the other side. If you don't like your fill, maybe you should have used a conditional order based on the mid or a stop-limit order. The best lessons are the ones that sting.