3D Viewer !!

Actually... Wait for it... There is one ;)
It's called marmoset viewer, look when you upload a model aside your vimeo and youtube embed import file feature, there is a marmoset viewer import feature.
Just go in marmoset toolbag, make sure to set the sky and model like you want then export as .mview and upload in with the marmoset viewer feature.

I used it on my last model see (2nd thumbnail) : https://www.cgtrader.com/3d-models/exterior/office/realistic-highly-detailed-luxury-hotel

Actually that would be great. On Sketchfab you can inspect relevant details, like triangle / vertex count, wireframe, texture maps, normals direction, see the object without post-production, etc. Also you don`t need extra-software, everything is done in the browser for free. The main issue is, that Sketchfab has its own market now so i don`t know how this works out between CGTrader and them.

As far as I know, you need Marmoset Toolbag to be able to export to Marmoset Viewer - it has its own format, unlike GLB or glTF2, which has wider support and almost any 3D modeler software can be used to create it. CGTrader already has a built-in online model viewer - the one we can see on the main page - but they use it solely for enterprise and business purposes. It is a mystery to me, why they didn't make it available for the sellers yet, together with realtime in-browser rendering. Maybe they have an exclusive contract with Marmoset, maybe they are afraid of model ripping?

是的