that's what I am worried about ... my guess is that even if I study diamonds for say several weeks I will still lack the expertise to really know, similar to how it takes awhile to rate a good suit, etc. .... I suppose one solution would be to find a gemologist to help but that would be costly I suppose, or RE the measurements on things like the crown and pavillion are there guidelines that you can give so that within certain ranges I can avoid what you are talking about? its really hard to just look at it and be able to tell if the proportions are right. most are not, but youll be able to tell by how beautiful it looks to you. if the diamond is spewing out beautiful colours, and showing great brilliance aswell you know its a good cut, and if it isnt you know it isnt. its that simple for you.(the buyer). go to a jeweller and look at a beautiful well cut stone, see how it looks and how beautifully the light gets diffracted through it and the colours coming out. then go shop and see how well the other diamonds you are looking at compare.