In his latest used games report at Mainichi.jp, Trader's Shunichi Kobayashi says that while the third Professor Layton game appears to be selling well (damn straight -- it was last week's number one game!), people aren't selling their copies back.
I feel the need to add here that anyone who does sell a Layton game back is part of the problem.
For recent PSP releases like Higurashi Daybreak Portable, Musou Orochi, Kenka Bancho 3, the store was able to sell used copies immediately after they got them in.
Over the week of 11/25 to 12/1, Gundam VS Gundam (PSP) was the top selling used title at the shop. Below it were Valkyrie Profile (DS), Castlevania Ubawareta Kokuin (DS), Quiz Magic Academy DS (DS), Super Robot Taisen Z (PS2), Way of the Samurai 3 (PS3), Chrono Trigger (DS) and Last Remnant (Xbox 360), in that order.
Regarding Gundam VS Gundam, Kobayashi says that the lack of a campaign mode may be what's making people sell the game back so much. The used copies sell in massive amounts, though, in part because of a price drop given to the game by the shop.
Valkyrie Profile sell-backs have also been on the rise, prompting the shop to drop its price as well.
For this week's new releases, Kobayashi says that 428 has seen a sudden burst in popularity. However, shipments for the game are low. He expects copies to be hard to find following second shipments on the 9th.
As a side note, I am currently debating changing the name of this series to something involving the word "recycle." Here in Japan, when you sell used product back to a store, it's called "recycling" the product. This naming applies to games too, so you'll see big signs at shops asking you to recycle your games.