Those are all great bikes, but boutique and not the utmost value if you are just getting into the sport. Somebody just starting out isn't going to appreciate any performance difference between a Cove or say a Giant (similar suspension designs), but they will have to may more for the name.
Also, there isn't a single company who allows warranty coverage to transfer owners when selling used bikes. If you buy used, you will not be covered by warranty if a problem arrises. Can you circumvent the system sometimes? Yes. Is it worth the risk? Not always.
If buying used, always inspect the bike in person, and bring a knowledgable friend with you to look it over if you can.