Also, are any of these products dangerous?
I'd say the worst thing about store bought spotters is
how the client uses them! Right outta the bottle and they use as much as possible!
IMO - resolve and oxyclean are two of the worst.
When I do my walk through, I always ask... Mrs Smith have you ever had a spot that seemed like 3-5 weeks after you spot cleaned it, it came back???
Well yes, Jerry I have... Well nucklehead it's coming back because the soap in your carpet is continuing to work. It's attracting dirt! If you are going to use store stuff, put a table spoon in a trigger sprayer fill the rest w/water. It will do the same exact thing.
It's VERY hard for people to understand less is better when it comes to carpet.
I also explain the difference between a dirt spot and a color stain(you should ALL be doing this). And what not to do, I generally tell them dirt stain/spot use what ever you want, just NOT a lot. If the stain has color - red, blue, green, yellow etc. the only thing I want them to use is peroxide.
Build trust, help them to help themselfs.