What is meant by cents while buying diamonds?

Answer 1

I think maybe you mean "sense" not "cents." While they sound similar when spoken, they have two different meanings.

Diamond sense means knowing how to choose a good diamond. Like above, it's education about cut, color, clarity, and caret.
To learn more:
http://www.thediamondbuyingguide.com/
http://www.foreverjewelers.com/help/diamondguide.htm
http://www.diamond.com/customer/jewelry_education.jsp

Answer 2

Likely nothing,
There are only 5 things that matter when buying a diamond: Color, Clarity, Carat (Weight), Cut and how much the recipient likes it. thats it.