I think it's more of a negative indicator. It's like turning up to a job interview wearing dirty clothes - unless you're a savant it's probably indicative that you don't give a shit or have some sort of other problems in life. But wearing clean clothes doesn't give you points because it's assumed to be the norm in that setting.

> "Is it clean and tidy right now" is a decent proxy for "Has this been properly taken care of in the past"

I don't think so, esp at selling time, I definitely expect that the owner has just made it look pristine. But the opposite is definitely true: if you can't even bother making it look clean and tidy when trying to sell, I'm pretty sure you've not taken care of it in the past!