Not entirely. If the coin is sufficiently rare, they will fake an apparently well worn/used coin with patina to fool the collectors. Classic example is the 1850 Shilling, which is mega rare. A few years back a Chinese seller was touting a load of them at £10 each. All appeared well worn and convincing, each substantially different. This seller made it clear they were copies, but the unscrupulous could buy one and pass it off as genuine.
On Ebay, the history of the seller is the most important factor, as you have pointed out before. In other auctions, for rare coins ask the auction house for provenance, and view even that with a jaundiced eye. There are now many coins in private collections that are fake because the collector was conned when he/she bought it.
As they all say: "If it seems too good to be true, it probably is".