I've never really looked at other people's carts to determine if they're healthy or not unless it's glaringly obvious one way or another.
I usually look and guess if they're single, married, kids etc.
Since starting back up primal, I do look now.
I hate seeing carts pushed by moms in their yoga pants, fit and slim with half their cart filled with healthy food.... while the other half is filled with sugary junk for the kids. /facepalm