As to the “demonstrations” I do not believe they need to be “faked”, just carefully set up. Freshman chemistry class presented any number of ion exchange reactions in which colorful precipitates were formed or removed (i.e.dissolved). In fact I once saw a demonstration by a Princeton professor in which he made a solution that changed colors three times in succession as he stirred it. Presumably, the reactants and products of several competing equilibria gave this effect.
The cleaning and painting and cooking demos on TV are carefully created to show maximum effect. I once bought the miracle scratch remover to “remove” a scratch on my truck’s fender. I think it was a simple wax. The type of scratches it could “remove” (i.e.hide) were very shallow surface scratches, not deep gouges that went through the top-coat and color coat down into the primer and metal. I got my money back. Now I use an orbital buffer, polish and wax.
The tarnish removers that use a metal plate and solution to instantly remove tarnish and polish silverware like magic are demonstrated with light tarnish using hot solution and, in some cases, time-lapse photography.
Remember what Mom always said, “If it sounds too good to be true. It is.”