I will most always put my loot for roll if I don't need it, however If someone tells me they will pay me or trade me items before I offer it then to me it a fair deal.
I pulled a +3 tome once and got 3 different offers for it. I ended up taking a trade for some gear I needed. I dont feel bad for it and matter of fact could have used the tome.
bottom line is that it is YOUR loot! Every player and every situation can be different so rather than speak in generality, I would say use your best judgment if the situation presents itself. To roll on loot and then sell it is Bullshiz in any form. But how many times have you seen a guild member roll for an item that another guild member in the group needs?
Whatever you do just be prepaired to be Blacklisted if you **** people off. Funny how this works though caus I have given so much shiz out and didnt get so much as a thank you, but I know had I kept it or sold it I would have never heard the end of it...