Guy, lets face it. when a person trys to sell you a diamond ring for a dime, chances are it ain't worth a nickel.
As a marine, you are going to be a rifleman first, and what ever you manage to agree on by contract, if they have such a beast in the marines like the air force, later. Anything, promises, mos guarantee, educational perks, enlistment bonuses, and any other offer you do not not get on the enlistment contract, wont exist.
Read everything you get on the contract twice forward, and once backwards to make sure its what you and the recruiter have agreed on. If it sounds to good to be true, it probaly is.
Think of yourself as a valuable commodity, and bargain well. I wish you good luck