So they're recovered and successfully identified 30-40% of everything sold on Ebay as stolen property? Wow, they must sure spend a lot of time on the internet... and driving around to seller's homes.
What I suspect is that they took a small sample size and extrapolated it... maybe let's say they had a representative percentage of .1% (in the real world probably even less) for a given area and found that .03-.04% of the original .1% that was sampled was stolen merchandise.
Obviously some items are more suited to be fenced through Ebay, for example you're probably not going to find may stolen cars offered, but for sure things like auto parts.
In the retail business theft is a major problem and it's not just some local mis-guided youths, it's profitable enough for it to be organized as a business model. Today busting a shoplifter means they are probably going to be looking for the ring leaders who have upwards of 100's of thieves working for them at any one time.
Ebay and CraigsList have replaced the local Pawn Shop and buying out of the back of a van... and neither Ebay or CraigsList will admit there is a problem.