Verbal Contract

My friend has a furniture wholesale company. A friend of his approached hime eight months ago saying hw is interested to learn about furniture business and offered to work for the company without pay. My friends accepted the offer and let him work for two months. At that point my friend’s company was about to open another office in different city. The guy offered again to relocate and help setting up the office. This time he was asking for $3,000 of salary. My friend didn’t agree on the amount but he did promise to pay him soem money. The he guy moved and stay in that city for 3 months. Now he is sueing my friend for breeching verbal contract and pursuing payment of $15,000. Is this a ligitmate case? What should my friend do.