Living in a scientific age, we must expect that the scientific method will eventually be applied to absolutely everything; how little surprising it should be that in fact commercial practitioners have been determinedly working in this area. But one of their most remarkable results is to copy the devil, and convince you that they don't exist. Or rather, to hypnotize you into supposing that it was your decisions that led to purchases you actually had no interest in.
The term for such practices, Weasel Ware, appropriately suggests the situation, in which an innocent customer is viewed, actually as an item of prey, a rabbit, who will not actually be eaten (unless we are talking about the vile reverse-mortgage business) but will be efficiently stripped of as much treasure as can be gotten without being detected.
For instance, you go into a sandwich shop and state the name of the sandwich you want. Without your realizing it, you have just begun a sort of "pick-up game", a two-person drama whose lines have been worked out in advance. Yours are simple - to say "yes" and "more" and "bigger"; the weasel's lines are designed to make your responses slide out of your mind without accidentally igniting an objection.
"I'd like a turkey sandwich, please."
"Certainly, sir! Will that be small, medium or large?"
"Small - oh, let's say medium."
"And will you want cheese with that?"
"Oh, that's a good idea."
"And what about a drink and chips?"
"Why sure."
"And is there anything else?"
"Why, no, I don't think so."
Until you terminate the conversation, every response is driving up the bill, and adding on overpriced extras you didn't want. It is easy to double or triple the price in this way, and all through the magic of Weasel marketing.
If you go to the barber shop, a low price may be posted prominently outside. While you are sitting in the chair, the barber may casually ask "And shall I shave your neck?", which seems such a wonderful courtesy that although you can't imagine why you would care about the one part of your haircut you can't see at all, you say, "Sure, why not." You find out why not when the weasel informs you at the cash register that the neck-shaving comes at an additional cost.
There's little to be done about this scourge, although it may be useful to make it more noticeable, since its strength relies in part on being unnoticed. I can only add, "Death to Weasels!"