Well the part about planes is pretty simple.. it has to have 3d depth, not single one sided poly deep.
Luckily, the main issue with DAZ market objects would probably be these one sided single poly deep faces. duplicate verts and edges are pretty rare from what I’ve seen in DAZ market objects. So are missing polys where there should be polys (although this is more likely then dup vert/edges.) Blender has some good tools for finding and repairing these but I don’t have the links handy for showing one how to use these particular tools. One also has to tackle learning Blender’s basics if going this route. All of the items on the checklist are basically on the ‘is it well made’ checklist, which is part of what one gets when buying for DAZ store, after the object goes through Q&A. Older objects might be a problem, Gen3 and earlier… but I haven’t run into anything noticeable yet.
One way to get an idea of the quality of the mesh is to go into the data folder and double-click on the obj itself, look at it in wireframe/shaded wireframe. It is hard to see dup edges/verts this way however, one would have to load the obj up into Blender and use it’s tools afaik.
Btw, objects one gets ‘for free’ are highly likely to have many, even all of these problems… high unnecessary poly count, missing faces, dup verts/edges, reversed normals… All of which can cause problems for any software package trying to work with the object. 3D printing just happens to be more sensitive then most regarding these issues.
Oh, the intersecting triangles beyond a certain point mentioned I believe is also referred to as ‘extraordinary vertices’ and refers to where there are multiple polys joining on one vert. In good design this should be kept to a minimum and also kept off of any edges or areas where it would cause a perturbance in the surface of the mesh. If one is necessary, it should optimally be moved back to a flat surface.
One thing I’m curious about with 3D printing is uniformity of poly size. Uniformity of poly size and poly count is a tradeoff. It is my understanding (and correct me if I’m wrong on any of this) that uniformity of poly size comes into play if texturmapping, as it makes it easier/harder to get a uv map that one can get even detail out of. If one isn’t worried about uv mapping a given surface, and doesn’t need high poly count for active distortion of the mesh, one can often cut down poly count by going non uniform in poly size. How this exactly plays into current 3D printing I’m not sure. Many DAZ objects have a very non uniform poly size btw to keep down on poly count.