[drc]

As far as authenticity and getting the item and getting it as described, the good big auction houses will be a lot more reliable than eBay-- thus it's reasonable that they would get higher bids. eBay can be a crap shoot sometimes, and people won't pay a premium for that. If it's 20% more likely that you'll get the item as described in Huggins and Scott than on eBay, sane bidders would bid higher in Huggins and Scott, in particular if you're plunking down thousands of dollars.

I also suspect that some well healed collectors and investors don't buy much on eBay. They likely think it's a circus, and prefer to deal with fewer but established sellers.

In an extreme case, if you had the money wanted to buy a T206 Honus Wagner where would you look? The big auction houses or on eBay? This may give a glimpse into the way said well healed collectors and investors look at eBay.