Try to buy something.

You walk up to the goblin and introduce yourself. And ask to see if he has any stolen goods. The goblin is immediately put off, and starts to nervously ramble on about how he doesn't deal in stolen goods. All the rambling has made him paranoid and quickly catches on as he found your kobold's hand in one of his pockets. The goblin suddenly screamed and made a fuss which quickly drew a crowd. The guards were on you before you could even realize what you did wrong.