All of the above plus the fact that while you might check the RRP with an online retailer, these days there’s a good chance that they don’t have it in stock. There’s been a huge impact of the economic situation on the used market, in some places invigorating it, in others killing it completely. It’ll no doubt revert in time.
Personally I buy used whenever possible because I prefer dealing with people to dealing with businesses/organisations. Ebay protect the buyer very well, while the retail sector doesn’t always do so, despite its legal obligations. This week I bought a very expensive unit (new) only to find it has a fault. The hassle involved in sending it back along with the implicit suggestion from the business that I’m being difficult/unreasonable is frankly at a level that makes me think it would be easier to keep it and fix it.