The problem with two sided polygons only happens if the front and back faces share the same vertices. If the front and back faces points to different vertices in the vertex list, there's no problem even if the front and back have vertices with the same numerical value, so in this case, you can't import into Poser with the option of weld identical vertices. You can find authomaticaly double sided faces just looking for faces that have exactly the same vertex indexes, you can then remove one of the faces, but which one?....

Stupidity also evolves!