This game has a safety function to help you avoid softlocking or otherwise ruining your save file. Although all items (including key items) are salable, any items sold will thereafter appear in Ed Edmund's (cemetery vendor in Ancient Battlegrounds) shop list, regardless of which vendor the item was sold to.

Inheritance glitch involves starting a game by dying without a Dragon Crystal instead of from the title screen. When dying in this manner, any items in Ed's shop list are carried over into the new game. This can be used to transfer acquired items to otherwise new files.

Saved games retain information about sold items, so you can simply load a file which already has the desired NG+ items sold, then die to begin a NG+ file.

When preparing a NG+ file, be mindful of any items sold; all items sold to any vendor will appear in Ed's sell list permanently until purchased again.

Japanese King's Field Wiki - Inheritance bug explanation: https://kings.wiki.fc2.com/wiki/%E7%B6%99%E6%89%BF%E3%83%90%E3%82%B0

szsk's page regarding his run using this glitch and route explanation: http://bmky.net/yarikomi/kf3_nta/ http://bmky.net/yarikomi/kf3_nta/chart/

Raz198's Shop List (includes pricing for all vendors): https://gamefaqs.gamespot.com/ps/197726-kings-field-ii/faqs/73670