Same for me, usually sales drop around this period.
Probably no link with that negative comment but probably better pay attention to it and make the model better and wright comment below it saying “have reworked the model and took care of the points, provided it to user for free” or something like that.
The density of the polygons is indeed very irregular and not that logic, the user could have see that in the wire frame preview so not completely valid complaint. Most would probably not get the model after watching those wire frame previews regardless the negative comment?
Rendering and textures do look great, I would make low poly retopomesh and bake those textures and provide it as a game model, probably would sell 10 times better.
I believe if you do bring it to market as an offline rendering model it would sell better if it would be sub-d ready.
Price for such model is ok but curent product has some technical disadvantages.
The thing is you better avoid combining collapsed sub-d meshes with regular meshes, instead combine the lower level mesh and make the regular mesh have support loops so they do not get round after applying meshsmooth. Then you can combine all meshes and apply one meshsmooth modifier to the model and have everything work out fine, that would be the situation most would want to have with this type of model. Also do not forget to remove or disable the modifier before exporting to OBJ.
About Vray plugin, it would indeed give a warning but the file usually still opens after ignoring it.
Anyway, to avoid problems you better always provide a completely native 3d max file setup with default scanline just in case, and mention in the description that it renders different results.