Is your feature request related to a problem? Please describe.
Non sell list.

Describe the solution you'd like
option to add items on whitelist/do not sell list.

Additional context
I think this was an option in the past. not sure I have not changed addons in ages and I remember having white list for seller addon. maybe its longer ago and was different addon.

but for example my warlock got 2 handed weapon for felguard to wear. I want it to not be sold.

There is a hotkey setting called "Toggle Item Under Cursor" in the game's Keybind settings. If you press it twice, the item will be added to the whitelist. Also, when you interact with a merchant there is a Scrap tab which shows you all the items you set as Useful and Junk and you can move them between sections.

Thank you for this, I've been having an issue with Scrap where it keeps selling [Time-Lost Artifact], a low level trinket that teleports you to the Timeless Isle , if you have Low Equipment check under filters. Thank you so much!!!

There is a hotkey setting called "Toggle Item Under Cursor" in the game's Keybind settings. If you press it twice, the item will be added to the whitelist. Also, when you interact with a merchant there is a Scrap tab which shows you all the items you set as Useful and Junk and you can move them between sections.