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.

It seems like there might be some kind of strategic direct defense. The possible victim could identify remembered triggers in (for example) a compliance situation, and then have a policy about how to act after such observations. You don't have to disengage; you could decide that you want to continue with the process. The extra level of reflection simply gives you more control.

Cialdini advocates this kind of meta-strategy in Influence.