Cleaners: Branded glass-cleaners are good, but please be sure that they are not ammonia based ones. These solutions tend to dissolve the film and the tint lasts less. Simple dish soap or alcohol based cleaners can be good enough.
Materials to use for cleaning: Avoid any kind of brush. Its better to use a soft cloth or sponge wipes to do the same. Always make sure that your cleaning materials are free from dust if you have used them previously. Hard sand particles can tear through your tinted film leaving a scratch on your window.
We do have people coming in to get a hand cut tint applied after removing their computer-cut tinted films.
We did not face such problems in the past and you should not worry about any crackling or delamination of any sort. We got you covered on that front.
As per the new Sacramento window tinting law, modified on January 1st 1999, it allows “clear, colorless, and transparent material” to be “applied to the front driver and passenger side windows for the specific purpose of reducing ultraviolet rays.” (Source: http://www.chp.ca.gov). As per the California window tinting law, the front driver and passenger window must have a minimum of 70% visible light transmission (VLT) with or without film.
If the stain is too hard, use dawn liquid detergent and water. Your last resort could be a blue clay bar and then applying some coat protectant on the affected areas.
Dry it up with a fresh micro-fiber towel and use high quality/quick detail spray to cover up.
Just imagine, when your friend sees your highly detailed car from outside and gets in to experience an OOTB dashboard and non-detailed interiors!