it's not a matter of fault but being put in a situation where they have to be compared to the mc's party, which is a shitty position to be in most narou-kei manga/novels. That said, her response is, of course, the last thing you would want to do. The promising newcomers aren't going away and souring your relationship with them out of fear of losing business to them isn't going to turn out well in these stories. IN REAL LIFE, yeah, businesses shit all over smaller and newer businesses all the time before they devour them as a matter of practice, but that ain't going to happen here.Why would they take any blame on this? The guild screwed up by double booking -- they should seek remediation from the guild.
Aside from that, it's a scavenger hunt. Were it not for Rein's skills, it would just be a matter of luck who found the poachers first.