From my experience of painting my own rims, preparation is the key
Just keep sanding the paint back until you get it real nice and smooth, you only need to take the clear coat off because paint best sticks to paint, or if youve got scuff marks sand it right back to the primer and use filler primer to get it nice and smooth again, then paint, then clear coat.
I got a real nice Gloss black on mine for all 4 rims cost under $40