Clarification: if you walk into the leather shop, with $300 burning a hole in your pocket, and see a nice jacket - and the guy behind the counter knows what he's doing (and gives enough of a shit) you will walk out of their, happy with your new jacket.

Are you assuming you walked into the leather shop with the intention to buy something? Or does walking in with a friend/partner who is shopping there count, but you wanted to spend that money on something else?

Saying there's no defense whatsoever was a bit of an exagerration; it's true that some people are more resistant than others (though not infinitely resistant), but even if you're weak you can always avoid the situations in the first place.

Do you have any evidence to back up these success rates on people who actually don't want to buy the thing (prior to manipulation)? I am highly skeptical that people are on average so easy to manipulate. I am not skeptical that there are many people who are marginal on whether or not to buy a jacket, and hence easy to talk into it. However, you seem to be assuming a level of irresistibility to manipulation that does not correlate with my normal experience. The world is full of manipulative sales pitches - and most of the people resist them most of the time, otherwise most people couldn't afford to eat.

I'm not denying there is a large contingent that is so vulnerable, merely claiming they are less than 50% of the population. If I had to put a confidence interval on it, I'd say the percentage was 1% - 30%, with the higher percentages assuming they are segregated into socioeconomic groups that I'm unlikely to encounter in my daily life.