Another benefit in using loupetroop and diamondbistro is that they don't take a cut. Plus, the regulars here are always asked by friends to help find rings. I always look here first and recommend.
Not charmy, but if you are referring to loupetroop, the site I believe was set up by the husband of one of the women who post here. It is pretty much all Pricescopers who buy and sell over there.
Yes, they are very legit. This is how most of us sell our jewelry that we no longer need. Of course, you have to beware just like you would for any onlines sales for "bad" people but these sites are safe. However, if you are not skilled with online sales and not savvy with buying online .... you may be better off consigning your diamond but they will take a cut of anywhere from 10% to 20%.