How did bilbo manage to keep from disclosing his amateur rating as a burglar?

Bilbo managed to keep his amateur status a secret by distracting Thorin and the others with a lot of questions.

"First I should like to know a bit more about things," said he, feeling all confused and a bit shaky inside, but so far still lookishly determined to go on with things. "I mean about the gold and the dragon, and all that, and how it got there, and who it belongs to, and so on and further."

"Bless me!" said Thorin, "haven't you got a map? and didn't you hear our song? and haven't we been talking about all this for hours?"

"All the same, I should like it all plain and clear," said he obstinately, putting on his business manner (usually reserved for people who tried to borrow money off him), and doing his best to appear wise and prudent and professional and live up to Gandalf's recommendation. "Also I should like to know about risks, out-of-pocket expenses, time required and remuneration, and so forth"-by which he meant: "What am I going to get out of it? and am I going to come back alive?"