Truth be told -- you can never truly guarantee a programmer’s coding ability just thru interview. Some are really proficient during the interview answering technical questions correctly left and right however, he/she may not be good in applying those knowledge in code. Some candidates are not so technical when answering the questions during the interview yet they seem to excel when they start coding. Most companies (overseas specially in Asia) have technical interviews and/or tests to assess how competent the coding ability is.
It’s a calculated risk you have to take. You will never know unless you try that person out. After all, there's always a 30 or 90 day probationary period? Goodluck!