I have some leftover ammo that I plan to sell, either here or on GB. Any concerns or areas where I'd get tripped up? Can I just sell it like I'd sell a gun case or scope? Some of it is rifle ammo and some handgun, if that matters. Thanks.

Post it here, it will not last.

Ask for their FID apon meeting up.

Shotgun and rifle ammo I think you can sell without any worries.

Handgun ammo - There is a section of NJ law that says it’s illegal for someone who does not have a valid FID to receive handgun ammo in NJ, so it’s possible a buyer who doesn’t have an FID could be committing a crime by buying from you.  When I’ve sold handgun ammo in the past I’ve just requested that buyers show me their FID (I didn’t record it or save any details, just asked to see it).