First of all I always tell them to discard the bottle because they never work.
Next I try to explain -if they care- that there are so many variations to what could happen. The fabric has Chemicals (the color itself, if we are not talking about a solution dyed fabric) the accident will bring more Chemicals (either food or drink dyes- natural or synthetic) or stomach contents which are also more Chemicals.
Now you have multiple chemical reactions going on and on top of that you have the folex/resolve/etc sitting on the fabric for a long period without being rinsed out. It has a very good chance to "bleach" out colors.
It happens sometimes when we rinse/flush the fabric, we have these spots popping out of nowhere looking like bleached out spots. Its all because they had done spot cleaning and the left over chemistry perhaps weakened the dyes and now its being washed away. I always try to find out before cleaning: was there spot cleaning done and was the fabric rinsed?
Also to help I always tell them what to use on spots/accidents: the single best product to use on any type of spots stains, is a telephone!!

people are alwaysooking at me like..huh?? I explain, we have a much better chance to remove spots if there are no chemicals introduced to it by the homeowners.