A strong relationship builder is someone who builds up the other person. One of the ways this is done through 'sincere compliments' and not through simple flattery. Generally people can sense that flattery is false and that there are ulterior motives behind it.
This is my favourite quote, "When you see a turtle on top of a fence post, you know he has got help getting there." I don't use that quote to suggest that you manipulate people, what I mean is that you use each other's strengths to advance.