If it really is the general consensus that paid content doesn't need a credit then I'm surprised and saddened. The Carrara gallery, in my view, is for sharing methods (in the spirit of help and cooperation) as well as the final image. The need to give credit where it's due is not only a courtesy to the original creators but it helps others learn from your efforts. Added to which by mentioning his creation you might just help the poor sod that modeled that widget in the foreground of your stunning render to another sale. I'd be furious if a publisher omitted to credit any of my work, even if they'd paid for it, because I make my living [ha, ha] from my work and I rely on others seeing it and knowing I did it. So, call me old-fashioned, but in my view, to not credit content (or for that matter plugins and indeed the other software used) is not only discourteous but risks an accusation of plagiarism.