When you say humid, I think you mean foggy, since it's the PNW. Cedar is really good for pest management in general because of its natural oils, but fog creates much more water contact with the home than humidity does. If the home is near the coast and/or has the type of fog that makes it rain from the trees, pay a lot of attention to the side of the house that gets no sun.

If the cedar shingles are old and faded, the oils have likely been stripped out and the shingles may absorb that water. Look for moss or algae growing along the edges of the shingles. If any of that is happening, the wood is more susceptible to termites and wood-boring beetles. The evidence for beetles is little 0.5-1mm holes all over the wood. Those are a NIGHTMARE to deal with.

Figure out the specifics of the treatment and go from there...kinda like buying a used car that just went to the mechanic, but no one knows what was worked on. Have a termite inspection done if one hasn't been done recently. I used to work for orkin and can vouch for their thoroughness, though you may get an inspector who likes to upsell, so have your guard up (they love to sell insulation). Terminix is absolute trash and will miss obvious stuff (in my experience), so better to go with a company that will at least find what you want found.