If you want to do normal alloys then it's easy to do yourself. Buy your self some paint thinner.. some sand paper (wet & dry.. 200 grit up to 800 grit).. some filler.. laquer and some silver spray (
einszett Car Care Products | Wash).. i used the silver wheel laquer as it's close to OEM for nearly all german cars...
Start by cleaning the alloy with normal car wash soap/water.
Then dry it and clean it again with the paint thinner.
Get the 200-grit sandpaper and sand it back to take the rough layer off (only scratch area)
Clean again with thinner.
Mix the filler and apply a small bit (if use too much then takes longer to sand off)
Allow it to dry
Use the 400-grit and sand back until nice and smooth
Clean again
If ok, then can move onto laquer, else apply more filla and repeat step.
Mask off wheel and tyre and anything else in the way (spend some time here!)
Clean again
Spray the laquer over the section - pressing the button on and off and NOT using a continous stream of spray
Alloy to dry
Once dry, get the 800-grit (wet!) paper and sand the laquer back until nice and smooth
Clean again
Spray with silver spray using a stop/start motion with the button
There you go!