The easiest way I learned that lesson is to see what some ex employees have posted about themselves in Linked In. It's like 'is that the same person I fired??'
Resume's are often a major fabrication or exaggeration. I don't care how it looks, make sure you truly test this person's skills if they claim to know a product. I've had people self rank themselves on a scale of 1-10 on various modules and wondered later, which curved grading system they were used to.