For a first time 'burgling,' Bilbo fails to meet the dwarves' high expectations with his performance, and some of the dwarves are fairly critical about his effort:
"Silly time to go practising pinching and pocket-picking," said Bombur, "when what we wanted was fire and food!" (39).
When the dwarves send Bilbo to find out about the light ahead of them, Bilbo does his best to steal William's purse from his pocket, but the purse squeaks at him and gives Bilbo away. Of course, Bilbo is then caught by the trolls and interrogated. Bilbo accidentally gives away the fact that he has traveling companions to Bert, which results in all of the dwarves' capture by the trolls.
On a positive note, Bilbo does find William's key to the troll hoard in which he, Gandalf, and Thorin all find remarkable elvish swords and plenty of treasure to appease his dwarvish companions. Bilbo's start as a burglar may not have been an admirable one, but the attempt ended well, with a little help from Gandalf!