30k to 50k is about right for salary, but you are right, he would make more depending on bonuses and commissions, which are up to the agent and what you sell (which is NOT easy). Lots (and I mean LOTS) of State Farm agents hire family members. Sean may be working there to bide his time while he decides what he wants to do or to put in the 5 years needed to train to be an agent himself. Right now he has the same job I do...poor guy(lol). Anyway, I like him so far but have to wait to see if he is for real.
As an aside about Roberto, he did open a State Farm agency in CA and had it for about a year, Farmer's courted him to become an agent for them and I would assume it was more lucrative and he went with them. It's tough getting started and hard to pay the bills until an agency takes off, which can take quite a few years depending on locale and how much time you are willing to put into it.