I’m not even sure which person we’re referencing. Are they advertising themselves as a professional or as an amateur/hobbyist?
I’m not saying I disagree that it’s important to have a back up. I just think if I paid a nominal amount for a photographer for something like a wedding, I wouldn’t necessarily expect that. I would be disappointed if their camera failed, absolutely and I probably wouldn’t pay them if they aren’t delivering… but I guess that could be because I have an understanding of “you get what you pay for”. I’m not condoning it either, but I do understand where it’s coming from and I have seen other pros that are fantastic, that don’t have a spare. It makes me worried but that’s their gamble.