We do not climb higher than a 2-step stool, so higher items will only be dusted w/ an extension duster. We only move light furniture that can be picked up with one hand. But we do reach any visible places either by hand or with an extension duster. Most homes have at least one chandelier or vaulted ceiling fan that we cannot reach by hand.
We cannot guarantee the results of mini-blind cleaning. Excessive build up may require ultra-sonic blind cleaning (we can recommend a service to you). We do try to dust furniture, shelves and knick-knacks so that their is minimal dust resettlement after we leave, but we cannot prevent this entirely.