I'm following this thread with interest as tourist visas to USA and UK have many similarities. Applicants to both must show a compelling reason to return, which means a demonstrable job (no working on the farm or the beauty salon), house/land with deeded property in his own name, substantial savings, credit cards. Obviously he would have a return ticket but red flags would be no hotel reservations in his name, no travel itinerary, he says he is staying with you, a family member or friend. There are Youtube videos on all this. Also consider a fiancee visa as the requirements are far less stringent and you go with him to the interview.