My contractor is installing the new Kitchen cabinets before the hardwood floor is refinished. Wouldn't it make sense to refinish the floor before cabinet installation? And they are installing the cabinets directly on top of floors that have drywall mud/dust and wall texture spray.

Also, does an underlayment or additional subfloor material need to be installed under the Kitchen Cabinets to make the subfloor and the kitchen floor the same level? My contractor is installing them only with shims. I'm worried that moisture could seep through the joist cracks and eventually warp my Walnut cabinets.

Should I be concerned or am I over reacting?

Thanks!