I'm not aware of a shipping provider which provides an insurance option which covers live material and plants. I would appreciate hearing if anyone has successfully filed a claim for lost or damaged plants. The USPS Priority Mail insurance information online does not mention plants specifically, but states it does not cover: "Perishable contents frozen, melted, spoiled, or deteriorated." My Shippo insurance likewise doesn't cover organic material of any kind.
There was a big discussion today among dahlia friends about cuttings they are receiving from different sellers. We have a consensus that USPS is too laggardly to use for cuttings. Especially as the weather gets warmer in certain states. We also like corrugated paper rolls or cardstock/cardboard boxes and tubes versus plastic clamshells, or even macaron boxes.