After you help someone, you can take all of their belongings to sell, except for a few items. For example, if you deliver Adrianne Avenicci's sword to her father, you can take all her belongings at her home. Or if you deliver Farengar's frost salts to Arcadia, you can take most of her alchemy ingredients. My question is... can all items in the game be looted without having to steal? How can I freely take the items at the Drunken Huntsman, or the meat shop at Whiterun? I am a big miser with gold so I sell everything. Kettles, bowls, cups, child dolls, wooden swords, etc.

There's usually a value limit. You can take anything that dosen't surpass that limit.

Horses are an exception to that value limit. If you help Katla with harvesting at the farm, she will allow you to use her horses.

Same with the guy at Riften's stables.