My approach is they're free to do whatever as long as they keep out of my way. That is, they're welcome to set up webs in ceiling corners, or in hard-to-reach areas that I forget exist. But if they try setting up a web near a place I frequent or things I often use, I'll give them a forceful relocation.

Once you hear them, you can't unsee them, even if you haven't seen them yet...

One might perform “preventative” measures like spraying for pests. This would be operationally different from killing them only when seen.

Traps. Mechanical, glue, poison, etc, are all available and don't care if you see the critter before doing what they do.

I won't use them for anything that doesn't pose a structural threat to my house (i.e. termites), but others do.

Subterranean termites are an interesting case. They usually live in a big colony that is not in your home, and just work in your home. And unless you live in a very sparsely populated area, that same colony is probably working from your neighbor's homes too.

When a pest control company deals with them in your home the poison they use is designed to not kill right away. It is defined to get on the ones in your home and be carried back to the colony with them where it spreads to all of them. Then when it kills it takes out the whole colony.

Note this means that even though they might be in several houses in the neighborhood whoever first discovers them in their house usually ends up paying to remove them from the whole neighborhood. That can cost a couple thousand dollars or more.

I wonder if anyone ever tries to take advantage of that? For example if you find you have subterranean termites give a neighbor or two gift certificates for a termite inspection, in the hope that one of them also has them and pays to get rid of them.

They really shouldn't be in multiple houses. The subterranean ones are supposed to create mud tubes up from ground to the wooden part of the house. Those should be noticeable for most people. There is another type, but those require a water source. So you'd need a leak in the exterior or in a pipe. It's fairly unlikely these circumstances present themselves at the same time for multiple houses in the vicinity.

What's the incentive for the pest company to do it that way, vs just kill the current ones/make the house unattractive (and thus expect probably to get business from some neighbours soon)?

Yep, diatomaceous earth is what popped into mind for me.

You set out traps for everything you'd prefer not to have in your house, just on spec?

How do you move around without sticking to a dozen traps and having a dozen others slam shut on you?

I think the parent was joking.

Optimism.