I just recieved a CD in the mail from an eBay auction that was listed as with "no surface scratches" and it has a deep scratch across the last four songs, along with other smaller ones. I played it on my computer and those songs seem to play OK, but I tested it with Nero CD Speed and there were massive C2 errors right at the section of the CD where the scratch is.

The problem is that the detection of the C2 errors is intermittent. I tested it 6 times - four tests had errors; two had none. Does this mean that this test is useless or just very sensitive? When they did show up, they were always in the same place, although one time there was a stray C2 error at the beginning of the CD also. I also tested it by ripping those four songs with EAC and there were no errors.

What do you think? I'm just worried that this CD might not play on more sensitive players.

If you are worried then, since it seems to rip OK, just make a copy and play that.

AFAIK, c2 errors shown in Nero CD speed are errors which are found and (usually) corrected at the c2-"layer" of the error correction. As long as there are not too many of them close together (look for the max value, can't really give a number, the less the better of course), everything should still be readable without error. The fact that some test runs don't even get c2 errors (could e.g. depend on the drive speed) probably means that it's not that bad yet. There are players where this CD could be problematic, and if it gets scratched a bit more the situation could get far worse, so better make a copy like pdq said.