Re: bad technique vs. resistance
What I do depends entirely on uke and my relative experience.
If uke is junior, I assume they don't know what they're doing and I tell them why they don't want to be doing it. This may include a gentle demonstration, such as moving slightly from my center and inviting them to observe how their rigidity has given me a direct channel to control their center. Or it may include a more active demonstration, such as showing how easy it is for me to punch them when their rigidity leaves them open. (With junior aikidoka, it's nearly always being too stiff.)
If uke is at about the same level as me, I feel free to adapt the technique to take advantage of whatever opening they've given me. Recently, a guy I was practicing with received the beginning of shiho nage with totally stiff arms. Rather than trying to complete shiho nage, I took advantage of the leverage he'd given me to throw an odd reverse-kokyu thing that never would have worked if he'd been receiving properly. To his credit, he immediately saw what had happened and loosened up.
If uke is significantly senior, I assume they know what they're doing and they're trying to teach me something. So I try to find a way to move them compatibly with the technique we're practicing without fighting their power.