I wasn't sure whether to post this or not, as it would technically be classed as second hand, but choicesuk do offer a full returns policy on these, the same as buying the item new.
They have opened the pre-viewed store, where they are selling off some top DVDs at bargain prices. These items may have been ex-rental at their choices stores. There seem to be some good titles at cheap prices.
But as always - price compare before you purchase!