Regrinding a camshaft makes it extremely weak. There have been at least 5 ppl that I know of on this site with regrounds failing. Other members have seen quite a bit more. I would give him his money back and take the cam and trash it before his engine blows up.
I would if I didn't tell the guy it was a regrind. If it was a situation where it was disclosed that it was in fact a regrind, I'd call the deal good.
1969 Chevy RCLB C10 350/TH400 SOLD
2007 Chevy RCSB 4.8 4x4 LS SOLD
2008 Chevy RCSB 5.3 4x4 LT SOLD
2010 Chevy CCSB 6.2 4x4 LT SOLD
2005 GMC CCLB DRW 6.6 Duramax 4x4 191,000 and counting
2013 FORD CCSB F350 6.7 Powerstroke 4x4