I always encourage people to do an audit of what is on every breaker when they get a new home (and make notes). It takes a little while, but when something like this happens, you know exactly where to look. It's harder to diagnose if you don't know what breaker the fixture is on.
Agree on the GFCI advice. I had that happen - the GFCI outside tripped and took out half of the lights in my kitchen. Whoever wired them put them electrically downstream of the GFCI. Took me days to figure out what was going on, because it didn't occur to me that the outside GFCI would be protecting my kitchen lights. And I wasn't trying to use the outside outlet for anything, so I didn't notice it was out.
I swear this is a regional thing. Where I live now, it is extremely rare to see a cart outside the return. But I've lived in other places where it seemed like no one returned their cart, ever.
I think it's a peer pressure thing - once it's the norm, everyone just does it. But if people started breaking that, I'd suddenly start seeing carts all over the lot.