This is surprising to me. I have stayed literally hundreds of times, not only for work but for pleasure, in hotels and motels that ranged from the Peninsula in Hong Kong and Ritz Carlton's All over the world to Motel 6 here in the states including some of the better ones like LaQuinta and I have NEVER had such an experience.
But having owned a hotel I can tell you that if you enter your room and feel it's not clean you should go immediately to the desk tell them and request another and tell them to make sure it's clean.
Just accepting it is completely foolish in my opinion.