I hear often about a Razor X or Y that is good or bad and so on, but lets put aside things like beauty,collecting and so on

What makes a razor a great shaver?
It is just that after being in this site for some time, and seeing AMAZING Lynn's DVD and His collection (drooling ) I hear many say about this or that good or bad

So, How do you tell if a razor is good? I also apply it for buying from E-BAY, Web sites , friends and so on