Even by a marksman's standard he's reliable to a degree that's rare, and no one can trace where he learned it: no paper trail, no prior guild, no training on record. He keeps to himself, says only what needs saying, and the shot lines up every time. He's covering a younger brother's tuition; once it's paid, he may leave the way he arrived.
A smaller guild means less time waiting at the back of a big raid and more contracts he can actually close. More contracts, more rank, more money. The math isn't complicated.