khazan99
Semi-professional cabbage collector
Y'all talk about hidden and invisible chests. I have no idea what you're talking about. I'll occassionally run across a chest someplace I never expected it, but I wouldn't even know where to start looking for something that's invisible.
The "invisible" chests are what all the NPC merchants use for inventory; the chests need to be in-game objects, holding the actual items that the merchants have to sell. There are ways to clip through the environment and see them below ground level.
In this case, it seems that when building the game, 3 of the chests that belong specifically to the Khajiit caravan merchants were placed by the designers close enough to ground level that your character can access them (and happily loot everything in them if you so desire). Note that anything looted does NOT count as theft, nor are the items marked "Stolen".
Video, if you'd like a bit more info (not the greatest in terms of narration, but, you get the basic idea....):