Whether or not I saw something has zero to do with what they're stealing and everything to do with where they're stealing from.
You do not steal from Mom and Pop shops. I will may not say anything to the staff, but I might pay for it or I might direct you to a better place to go steal.
If I see something in Walmart, no I fucking didn't. I don't care what it is.
Edit: based on the reply. It's a good point, but not something I've personally run into so it's not something I've had to consider. I've seen idiot kids doing idiot kid things. I've seen people in need. I've not seen a gang or tweakers stealing from a local shop, only large retailers (no I didn't, I do not give a shit) or individuals (I give many shits about this and my response ranges from stopping them to getting evidence to give to the owners depending on more factors than I can list).