It depends on your country of residence. If you are a US resident booking in SEA then insurance is never included (at least with Priceline). If you live outside the US then it may be included. It depends on the deal. You need to review the deal. If it doesn’t say, assume insurance isn’t included.

Also note that there really isn’t the concept of a deductible or excess when renting in the US (unless you are relying on your personal auto insurance policy for coverage). It’s either full coverage or no coverage.