Examples of what OP is specifically looking at could help the discussion.
Eg.. just randomly pulling an example from one of the referenced sites, not quite 10yrs old (9 yrs), but in the price range mentioned. You could ask something like the linked below, vs. similarly priced CAAD option available new today CAAD Optimo Tiagra

https://www.theproscloset.com/collec...52cm-bike-2010
vs
https://www.cannondale.com/en/USA/Bi...ntid=undefined

using a Trek CF used example in similar vein:
https://www.theproscloset.com/collec...58cm-bike-2009
vs.
https://www.trekbikes.com/us/en_US/b...Code=red_black