Exactly the same reason you should probably clean the rest of the house when you're selling it.

Theoretically, the price of the house before cleaning should be equal to the value if the house after cleaning, minus whatever the cleaning costs. In reality, you'll get much less for your house without cleaning it, because human emotions.

We had a contractor doing repairs before we sold our house. Without being asked he took an orbital sander to the wooden hand railings along the stairs to the front door and said "people really notice this".

A family came for the tour and before walking in the father put his hand on the rail, looked up at the house, and said "this place seems well maintained". Then they bought the house after a small pleasant (for us) bidding war.

The contractor earned his high rate and then some.

> because human emotions.

If I tour a house with pet urine stains all over the carpet, it's only logical to conclude that the owner is likely not maintaining the rest of the house to a very high standard.

It’s not just emotions, it’s a sign that, when presented with something annoying that you should do but not strictly required, it shows that you pushed through and did it anyway.

It doesn’t prove that you’ve been generally on top of things for the lifetime of the house but the inverse situation where you couldn’t clean one time for guests sure doesn’t.

It's not just emotions, it's also a matter of time and uncertainty.

I've been in a buying situation where my old lease was expiring soon, I had a second kid on the way, and the last thing I'd have wanted is to buy a place where I'd have contractors milling around for weeks or months to make various repairs. I was willing to pay a hefty premium for a place that's in a move-in condition.

I don't think this extends to "you'll get $10k less if you don't vacuum", but it's a common courtesy on a million-dollar transaction to maybe not leave a mess.

Having recently bought a house, I love thinking about things that increase perceived value relative to cost (more so because they're nice to have, not because we plan to sell any time soon).

A few things we changed right away: - new mailbox (replacing a rusted 30+ year old one) - lots of landscaping work (the majority of which I can do myself) - installed a wine fridge (I always felt it gave the sense that the kitchen was upgraded when we were touring places) - replaced old door knobs with modern matte black levers; ~$50 each

The house was built in 1968, so it's been interesting to think about all of the small things that make it feel dated that can be changed for not much money.

> In reality, you'll get much less for your house without cleaning it, because human emotions.

It's trust, because if the previous owners can't even bother cleaning it up, what else might their neglect have done to the house? Do you need to change the house wiring, maybe verify if any new paint job is hiding mold or infiltration... All that is the cost of uncertainty and uncertainty grows with distrust.

This simple procedure increases the selling price of everything. Just a fact.

It's perfectly rational to assume someone who didn't bother to clean the house before selling probably didn't take good care of the house in other, less visible ways.

People often confuse "irrational" with "rational on inference given incomplete information"

This is the latter.

See also: stereotype accuracy

See also why houses are often painted when being staged for selling just so that the new purchaser can paint immediately after with their preferred colour. Wasteful but it works.