It depends on how much paint and what kind of paint. Some come off easy and some are extremely difficult to remove. Once in a while it can be a major job. Even different colors vary in how difficult they are to remove.
Fake snow might be easy or difficult. Recent snows are easier to remove than in the past. If it is high on the window it is more difficult. You would have to try it to know. If it is inside you might need to put down a tarp.
If you have to put in a lot of work to get it off, don't you think it might be worth something extra?
Some people won't like to pay more because they don't like to pay more. Some will think it is easy. It is always easier when the other guy does it. Customers do tend to under estimate the job.