If a deal looks too good to be true, unfortunately, it probably is. Be honest and realistic. Rank carat, cut, clarity and color in order of preference before you shop. There is no or wrong order. It's a personal decision.
Diamonds are unique, but they are also a graded commodity.
The two most highly respected grading labs, GIA and HRD, adhere to strict standards and provide a subjective and unbiased evaluation of stones. Take your time. Don't let anyone rush you into a diamond purchase. You'll save money and time in the long run, by holding out for just what you want.