I don’t know if anyone has found or has a good way of cleaning the edges of clothing made using the extraction method I know that you can play with the poly count in remesh but I have found it hard to keep good topology and shape I keep having something that becomes unusable
The polygon structure of a mesh extraction is always going to match that of the source model. The exception is the edges, which of necessity triangulate any time your mask edge cuts across polygons.
The way to avoid that triangulation is to make sure that your mask edges follow an edge loop in the model.
Where that’s not practical you might wish to try a different method of mesh generation. For example, you can use the Topology Brush to construct an entirely new model that follows the contours of the original but has whatever edge flows you wish. http://pixologic.com/zclassroom/lesson/topology-brush-accessories
I am guessing it’s rough edges you are concerned with? If so, try running the Smooth Groups Brush along the clothing edges before extracting, it really does an amazing job.
First, duplicate the subtool you are extracting from. Make your mask and Ctrl+W to make a new polygroup then go to Polyframe view. Now open Lightbox>Brushes>Smooth Brushes folder, grab the Smooth by Groups Brush. Clear your mask and rub this brush at lowish Z Intensity along the edges of the new group. Mask the group again and then Extract. The edges will be crisp and sharp.