Sites like this (not just cars) are a dime a dozen. They just crawl the web for car ads and repost the pics and info. The best thing to do is if you see a car, then go to ebay, CL, Hemmings, Kiljiji, etc. and the original ad placed by the actual owner will be there. Usually though, it will have been long expired.
These kinds of sites aren't brokers, so I don't know what they do with your information if you hit "contact seller." I can't imagine they follow through, I would think its just for ad traffic $$.
Case in point, the FC7 1970 Super Bee just listed on FBBO is also an ebay ad, now shown on "TopClassicCars". If you google this, I'd bet this car shows up on 15 websites, all taken from the ebay ad. And the owner didn't actually place them there.