I guess the moral here is to ask exactly what they are going to do before you let them near you. This is a tactic that has worked really well for me in the past - although it has upset some consultants when I disagreed with what he thought he was going to do and walked out. Ultimately it's your body.

Now, I once had an ultrasound of my bladder and the woman was commenting on my ovaries (a follicle was rupturing so it was kind of nice to know that everything was working the way it should). I guess technically she maybe shouldn't have been looking but to be honest, it really didn't bother me. If she'd tried to do a pelvic exam or an internal scan then I would have had an issue but if someone wants a quick squint at my reproductive organs with an ultrasound I don't have a problem with it.

The issue here is finding out your comfort level. You now know that you are uncomfortable with unnecessary womb-scanning so, if you're ever in the situation where it might happen again, you make sure it doesn't happen. If there's a good reason for it happening then the doc/technician can discuss it with you then.

I personally don't let dentists go near my mouth without knowing exactly what they are planning and why. Last time I was there, the dentist defended his treatment decision by showing me my XRay and explaining what it meant. In general, health professionals (and car mechanics) like you taking an interest and are more than happy to show you what's going on and discuss it.