Centari vs American Finishes Paints

What grit sandpaper are you using? Too coarse and your finish won't look as shiny. Not sure what you mean by 'thin coats'. If the paint is reduced too much (too thin) it won't have the proper gloss and it may soak into the old paint which also will affect the gloss. If you don't have the proper film build (total thickness too thin) it won't be as glossy either.
I can't remember the recommended time frame for buffing Centari. Should be on the label. Generally, the longer you wait for it to cure, the better enamel buffs. If you just laid down a couple of thin coats you better wet sand with 2000 grit or you'll buff through it.
Dallas