In the best of cases, this will be a teachable moment, and they will say, “You learn something new everyday.” In a so-so case, they might notice the lack of embalming because the body won’t be hard. They won’t know about the vault (because who even notices the vault anyway?) And they’ll focus on the box or shroud. If you’ve added a story like a family quilt or an artist’s or children’s decorations to a simple pine box, they will be charmed out of their judgement / criticism. And in the worst case (where things out of the ordinary aren’t accepted), if they are friends, they’ll keep their critique to themselves, and if they are not, you will know them by their noise.