To my mind the one recommendation for using sand paper is ill-advised, even if it is a high grit wet/dry sandpaper. However, I haven't tried it so maybe it works like a charm.
What I have done for a bike that I bought used and someone "ruined" the gorgeous original paint job, was used acetone and it worked like a charm.
Keep in mind that the clear coat paint quality is a "buffer" zone to the coloured paint underneath the clear coat. Typically the higher priced bikes have better quality clear coats.
Anyway, another thing is that the longer acetone comes into contact, the deeper it seems to "melt" the paint away. I used a rag and did kind of a two step process of doing small sections and using a clean rag for the second pass to take away the residual offending spray paint. Worked for me!