That guy was robbed by a failure of the markets to maintain a semblance of rationality. Once burned , twice shy. Very few people would assume an ETF tracking the entire market could suffer illiquidity of that magnitude. The designated market maker was a dick.
The lesson here: if you need to replace your brakes, have a mechanic do it, unless you're a mechanic. If you need to replace that toilet, let a plumber do it, unless you're a plumber. If you need a liver transplant, let the surgeon do it...just let the surgeon do it. Brokers may be the scum of the earth, but if you plan to put a good chunk of your net worth into a position, do it with a full service broker who makes sure its done right start to finish.