Commitment and consistency is really really good shit, but it's not for everything. Getting confirmation is fantastic for things inside their Locus of Control and "Locus of Observation", but not so great for things on the outside.
You really can put the cookie down. Really - you can. You might be really tempted not to, and you might even choose to eat it, but if someone put a gun to your head, you'd drop the cookie right quick - it's inside your LoC.
And that's why it's a great time to use confirmation. It puts pressure on them to do it, if they don't, you know ahead of time, and you can debug from within a "why won't you do it" frame rather than a "why doesn't this magic of mine work" frame.
While controlling how ticklish you are is probably outside your LoC, people generally have access to their anticipations which are good indicators of how ticklish you'll be. While it'd still probably be a bad idea to give then an order to be ticklish, confirmation is still worthwhile. It still gives you early warning on failures, the chance to debug, and additionally, it ups expectation (yay consistency!) when you get a positive result.
And yet, there are times when asking for confirmation will hurt your odds.
In order to be confident, you often look for the possibility of failure. If you ask someone to confirm something outside their LoC but inside LoO, you're placing a bifurcation point in their path, and you better know which way they're gonna go.
If the person cannot reliably predict the success of the suggestion through introspection, you're taking risks that you needn't take. If they can't introspect (well), then you don't get (much) information, and to the extent that they're aware that they can't introspect, you're likely to actively cause problems.
If you ask someone to confirm your 'magic' (i.e. outside of LoC and LoO) suggestion to raise their body temperature, then that's just asking them to consider it not working - which we know is bad. And this for no benefit - they can't actually confirm it's going to work anyway.
On borderline cases, you can weaken it a bit. Confirm that they understand, or that they desire for it to work, or that they could imagine it working. Certainly don't punish them for incorrect predictions - this causes more attention on failure. Anything you get them to say from within the "it's going to work" frame helps commitment and consistency by getting them fully into the right frame.
You'd rather they just give their first impressions without responsibility, not their consensus after layers of rationalizations are added. First impressions are more informative about what their state was before dicking with it, and it doesn't change things as much. Failure to get it right is a lot less worrisome if its just first impressions (it's just what came to mind automatically, not like "they" did it...).
And on the cases where its just not worth doing at all, specifically avoid it. Have them think no other thoughts, let them know it's not important whether they agree. Give the suggestion and distract.
It's so fun this way. If someone is critical enough that you know you can't win them over completely, just get your thoughts in and change the subject. "I know you aren't going to agree with me, and I'm not going to ask you to agree with me or even respond. I'd just like you to hear my side and let it roll around back there - blah". Then leave. It seems to put them in a position to be receptive to finishing the job later.
And I use it on myself a lot. I'm very much an overthinker that will shoot myself in the foot with autosuggestions, so this is great for me. My favorite way of inducing lucid dreams is to simply say "I'm going to have a lucid dream tonight" and then think about something else before I start to chide myself for spouting bullshit confidently. I just have to take a moment to clear my mind so that I can give my autosuggestion in a 'matter of fact' way, then think of something else. No staring into space, no mental imagery - just cut to the chase: Focus on the suggestion, and don't think opposing thoughts.
If they can do it, get them to just do it. If they can confirm it's going well, have them confirm. If they can't do either, then have them do nothing but hear the suggestion.