Like most disciplines, it's better to not have an unwanted behavior begin than to have to train it out of them. When we began this my fluffy was just less than a year old but we had a great start with what we were doing. A few of my rules: No dogs in the kitchen . . period
No table scraps are fed
No food other than at meal time except for occasional kibbles
when training (and a few isolated exceptions)
Crate training began at 7 weeks when we brought her home. When we left the room, she was crated. When we returned, we'd let her out. She never had the opportunity to get out of hand or do anything without supervision.
The two commands that were used were "leave it" and that two letter word that we all know to mean immediate disqualification from a HT or FT - "NO!" By simply setting up tempting situations like a sandwich on a plate sitting on the coffee table or a bowl of potato chips on the floor, when dog shows an interest they get a verbal correction and it certainly doesn't hurt to have a lead on them. The repetition imprints the behavior, and verbal praise lets them know they made the right decision. My dog is characteristically submissive and I think that it helps for this discipline. This is what I figured out for myself because at the time we didn't get into the specifics of the actual training of the service dogs.
Not wanting to give you any bum scoop, I just called them to get the real story and I wasn't too far off. They get the candidate as an 8 week old pup from a breeding designed with service dogs in mind. From day one the pup is on a leash that is attached to the handler at the waist. Where ever the trainer goes, so goes the pup. A choke chain is typical and when out socializing any distractions are addressed with an appropriate tug on the leash, so once again, the constant supervision doesn't allow for the inappropriate behavior to begin. When the opportunity presents itself, the correction is immediate. We didn't have time to get into the entire progression, but it lasts for 18 months at which time it's determined if the dog is suited to move on to another trainer for the next phase of more advanced training. So anyhow, I got a SH that doesn't snitch my lunch.