I accidentally low-rated a script when my intention was to give it a high rating. This occurred because the one-star rating shows up as a default rating in the rating dialog window, which pops up after using the script a few times. My thinking at the time was "Yes, I would like to rate this script," so I clicked the rate button, expecting further instructions on how to proceed. Instead, the (unintended) default rating of one star was immediately entered. This could be happening frequently. I doubt that I am the only user who is accustomed to more guidance from dialog windows.
If you know the recipe's number (aka its ID, MID, or MacroID),
you can go to its web page and change your vote there.
For example, recipe 101275's web page is
http://fold.it/portal/recipe/101275
It would also be useful to say on pages like
http://fold.it/portal/recipes
http://fold.it/portal/recipe/101275
that 5 stars is the best possible rating.
I know that I have done exactly the same as georg137 in the past.
The rating method isn't immediately clear.
In addition, I think that ideally any one player should only be able to rate a script once.
Currently you will get the opportunity to rate a script many times and if you do that it could skew the actual valuation of that script.