I made a similar response below but how can any amount of interviewing give me anything but a vague notion of the amount of value they will provide the company

I made a similar response below but how can any amount of interviewing give me anything but a vague notion of the amount of value they will provide the company over the next twelve months. I assume that their previous employer, who had them working there for years, is a much better judge of value they can provide. So if I am offering more than that, I don't see how I am not valuing the candidate.