Very, very few Marine applicants get a guaranteed job (mostly those with college degrees or extremely high ASVAB scores, applying for certain, designated technical specialties).
A vast majority of Marines are enlisted in a general field (such as Avionics), and will have their actual job (MOS) designated during basic training. One must remember, in the Marines, one is expected to want to be a MARINE, first & foremost. MOS (job) is a distant second.
For more details the article, What the Recruiter Never Told You.