They seem a little low until you really look at the prices of last year’s bikes. A 2016 Speed Concept 7.5 can often be found for about 75% of list (3 vs 4,000$). Team discount through Specialized and other big brands are also usually at least as much. Now somebody’s used bike with no warranty, worn components, no title (it might be stolen),… represents a pretty big risk to the buyer. For example, on my road bike, I am on my 3rd warranty frame from Specialized because PF30 was just a stupid idea. If I had bought that frame on Ebay it would have been a total loss to me.
I figure a relatively new, really clean and well maintained bike is worth no more than 40-50% of list. Now if you go to EBay you will see lots of used bikes priced quite a bit higher, but those tend to be relisted time and time again. Nevertheless, people are free to charge and pay whatever they feel comfortable with.