I just show them when I've done the job.
I have the camera on so I can check on my progress, to see if I've got all the crap out, when I'm happy everything is clear I film it. Some customers will hold my phone and I just say, "watch this, see what you think "(use discernment!!). Chuffed to bits usually. Others I just show the clip, happy with that.
The reason I don't show them BEFORE I do the job is that much of the gutters maybe not be very clogged up and so may feel aggrieved at paying for,what they deem, to be not much work. You could quote an inspection price I Suppose? Personally I don't bother with that.