CD's don't and never really did. If you bring in an early CD (like from the 80s) you can get a nominal amount because CDs were rare then. If you bring in a CD from the last 10-15 years they are nearly worthless. Most shops ended up shredding the extra.
DVDs have a bit of crazy market. Some distributors (Disney and Criterion especially) do a short limited run. The 2nd hand stores rely on these gems in a big box of junk to make profit.