Discogs proposes me a CD Box at 25 dollars, I confirm the order; they send me a modified invoice including shipment (not mentionned at the onset) 25 + 25 = 50 bucks ! I sent a cancellation message, this is plain rip-off !!
That's not Discogs wrongdoing, but the individual seller's policy. I use both eBay and Discogs only for very specific recordings (classical and pop) as shipping cost tend to be sky high (as in 'first CD $15, every additional CD $3') for international shipping. Make sure you always check the shipping cost *before* you purchase anything on Discogs. Amazon is way less expensive for second hand CDs. It's mostly the UK, France and Germany sites that offer the best deals for me (alhough the shipping cost from Germany also tend to be high, which is interesting as I live about 4km from the German border

). US sellers often do not ship to Europe.
One also has to realize that the demand for second hand (and new!) CDs has plummeted in recent years, especially for classical titles. Second hand classical CDs are really flooding the market, everybody who tries to sell second hand CDs knows that. That's probably why less and less sellers list these on the various Amazon sites.
The nice thing about this is that OOP titles that were really expensive a few years back can be found at much lower prices now on Amazon. Yesterday bought the 3CD Deutsche Grammophon sets of Orff's Antigonae and Oedipus Der Tyrann from the 1990 20th Century Classics series for €10.50 and €16.50 including P&P (The latter from Amazon.de which had a shipping rate of €7 for this box).