hello mate,to be honest,its not hard or to polish them out,depend how bad they are.... i did few cars mean lenses,if they really bad you start with 800 grid,then 1200,1500 2000 and to get best result i use 3000grid 3M pads,some people using say only 800 and prob 2000 and polishing... the reason why i use many different sand papers is to get perfect result,coz its plastic you dont wanna scratch it,you wanna go trough smoothly,in that case different grid sandpaper wont leave scratches on lens,also when you buffing down use a lot of water to cool it down and 1800rpm its tops,if you go to fast plastic starts melt,you dont wanna do that dont you? so,i hope its help for you,good luck!!!