Whenever you buy a car you should inspect it, check the documents and, if possible, take it for a test drive. You may also do checks for unpaid finance if you are concerned. If the price is right and everything else is in order, you can buy. If not, you should walk away.
If you want a car at trade price with no warantee, it's worth visiting a local car auction or two. Buying cars like this is risky but, as long as the price reflects the risk and you can spot a worn out car, it's worth a try. You should not buy the first car that you look at and you should not bid until you've been to a few auctions. At most auctions you can look under the bonnet but you don't get a test drive before the sale.
I've never heard of County Liquidations but what they are doing is not unique. It is important though not to bid for anything that you've not seen.