My problem is only with Smoothon 300 resin with their RTV rubber and spray can mold release. The parts come out with an indestructible glossy sheen. I'v tried thinners, strippers, alcohol, gasoline, every strong chemical I could find around the house. Even swimming pool acid. Nothing works.
Thought there might be a product I didnt know about.
Did you know that car paint shops sell a very fine steel wool that can be used instead of sandpaper. Very quick to key up the surface of any complicated shape. It comes in various grades.
I've found that once resin parts are flat primed, they will be flat when finished painted with flats. I do use alternating enamels and acylic method: base colors enamel and weathering and rusting, acrylic.