No, you cannot confirm willingness.
It is empirically demonstrable that we use non verbal behaviours from others to gain knowledge of their subjective state. I've given an example of such a test in my response to Trinity above. Any skepticism you engage in at this point would leave you in a position of not being able to know that other people around you have minds. There is a certain irony here. If dismissing non verbal behaviour as an indicator of other minds and emotions leaves us not being able to know how others around us are feeling or even that they have minds at all then this actually supports the case that these are our main indicators.
That's completely false. By your logic, I can then proclaim a robot a willful being, because it shows behavior of some sort(which it is pre-programmed to show). That's sheer absurdity. Just because certain behavior is taking place, doesn't mean there's a will behind it. This behavior could very well be concluded as "the sharks' body need X, when they show Y behavior." There's no need to invoke any WILL at all. And, as I said, you're pretty much assuming the conclusion there. I showed you how behavior does not necessarily imply willingness. All you had is "well, hours of observation!" Well, I may observe a robot all my life, and the fact of it showing behavior and me observing it for a long time won't make it any more willful being.
If my cat jumps on me in the morning, looks me in the eye, puts her paw on my arm and then pushes her head under my hand can I know from her non verbal communication (which she has initiated) that she wants to be stroked? Of course. If she sits next to window, puts her paw on the latch, looks at me and meows can I know that she wants me to open the window because she wants to go out? Of course. If I denied that then I couldn't be sure that any other minds existed at all because I would need to extend that same level of skepticism to everything to avoid special pleading.
I can conclude that, because I wouldn't have any reason to think you lying.
If I don't have a mind then I can't be lying to you either.
.. the fact that something nods and smiles, isn't a proof of willingness. I've had toys that nod and smile. That never convinced me of them being willful beings. I'm not saying behavior CANNOT SHOW willingness, but that behavior ALONE DOES NOT PROVE willingness, because behavior is also consistent with non-willful things(robots can exemplify behavior ; toys can ; cartoon characters in a cartoon animation ; etc.)
Behaviour is most certainly evidence of willingness because once you dismiss it as evidence then you leave yourself in a position of not being able to know if other minds exist at all. And why on earth would we use behaviours to express intentions to others if they are not evidence for the recipient of the feelings behind them? I haven't denied that we interpret one behaviour in light of other behaviours.
I'm driving down the slower lane of the motorway when I realise that it turns into an exit road. I want to move into the next lane to avoid leaving the motorway but there is no gap. I signal, hoping that some kind person will let me in. The car next to me remains level and doesn't slow down to create a gap. I look at the driver and see him staring at me and shaking his head. Can I know just from his various behaviours that he lacks the intention to let me in and more, fully intends to not let me in? Of course. The only other logical option is that he has no mind at all.
You know it by you yourself being a human being and expericing personal will, which you can extend to others of your specie.
But that isn't the case as the cat example demonstrates.
It's not solely because you observe others behaving.
What can you do, other than watch others behave?
That may be a reason, but not very conclusive one.
Empirical studies demonstrate otherwise.
The same applies to animal behavior - just because they show behavior, doesn't mean they possess personal will. It could be in support of that conclusion, but when coupled with something additional, for this premise on its own is not sufficient to arrive at "animals have personal will!" Because something showing behavior is also consistent with non-willfulness.
Its based on observing a range of behaviours in context. I've never denied that. But it is still most certainly based on an observation of behaviour.