And even if he has made a deal with a Big 5 publisher (which is what I assume you mean by legit deal), what is going on behind the scenes?

I know a lot of authors with agents who actually aren't shady who still feel doubtful about their agents' actions and whether their book is being pushed enough or their rights are being protected enough or their money is coming when it should or whether their next book is being ignored and so on and so forth. I can't imagine going into an agent/author relationship already doubting the agent.