I charge a substantial cleaning fee, and personally, I would not mark down for this, just as I wouldn’t mark down for other normal-use occurrences. The same goes for normal mishaps resulting from the use of other appliances like refrigerators, barbeque grills, and toasters. Only if the mess was egregious and truly slovenly would I mark down.
There are in-between situations, however, especially from new guests. They may have shown effort in some areas, but overlooked others. With those guests, I may not mark down or comment publicly, but offer some gentle advice in the private section of the review.
However, every host has different fees and requirements. I’ve even heard of hosts that don’t charge a cleaning fee and require that the place be left as it was found, just as long-term tenants do in an apartment.
The important thing is that requirements are clearly spelled out so that there is no doubt as to what is expected. Your requirements should be clearly listed in your House Rules, and readily accessible before booking.
As far as your peace of mind goes, I’ve found it helpful to remember those wonderful guests who have gone above and beyond to leave your place in spectacular condition. The minor, “extra” mishaps of other guests even the score.