Water first
Every job starts with where the moisture comes from. Liners and machines come later, if at all.
Diagnose first, then do the least work that will last
Many people find out something is wrong under their house second-hand. A home inspector's report says "standing water observed" or "vapor barrier torn". A musty smell comes up through the floor in November. The next step is often a sales visit, and it is hard to know whether you are being told what the house needs or what the company sells.
We think the honest answer starts with the water. Find where it is coming from, whether that is a downspout emptying at the foundation, ground sloping the wrong way, a plumbing leak or bare soil, and fix that first. The EPA's own moisture advice starts in the same place: fix plumbing leaks quickly, keep gutters working, and make sure the ground slopes away from the house.
Then we do the least work that will actually last. Sometimes that is a new ground cover and nothing else. A small Washington State University study of new Northwest homes concluded that, with proper site water management, both vented and sealed crawl spaces can work. The EPA's Indoor airPLUS program lists homes in a marine climate, which includes ours, among the exceptions to its sealed crawl space recommendation. So we do not tell every homeowner they need encapsulation and a dehumidifier. When a properly laid vapor barrier and a drainage fix will do it, that is what we recommend.
When sealing a crawl space is the right call, we say what comes with it. In that same WSU study, in test homes in a higher-radon area than Whatcom County, radon in sealed crawl spaces measured higher than in vented ones, and Washington's code requires a radon system and a continuously running exhaust fan in a crawl space without vents. A sealed crawl space is not radon mitigation, and we will not pretend otherwise.