Look, if you know anything about cars and how they operate there's enough information given to make an educated guess that has a 99.9% chance of being correct. The o n l y way her car would have any reason to need 91 is if she had an aftermarket turbo or supercharger. The chances of that are extremely low to begin with, but drop to practically zero because no aftermarket manufactures make a kit specifically for the Gen3 Mazda 3 2.0L. I'm not some uninformed random person, I'm literally building a turbo Mazda in my garage.

I made a perfectly reasonable statement that she is wasting money because she is. Many many people think higher octane = good. The only reason I started to get downvoted was because of hardcore feminists mad that I was insinuating a girl didn't know about fuel ratings. The angry PMs I got from them show that. Then you know Reddit, once they see someone downoted, that person is immediately the enemy and the dogpile of downvotes starts.