It is very possible that the customer would not have understood your kind help. If she did not have the concept before hand it might be too difficult to get it in an instant standing at the counter.

I'm one of those who always gets in trouble for offering her
"helpful advice"....

In years past, I would have said something. In the past decade I have learned to keep my mouth shut. I have been blasted enough and there is not need for me to put myself out there.

Another big mouth here! LOL it seems we have a board full of them hahahaha
Turn it around- I would love to know from someone who had more experience or prevents me from making a costly mistake.
I've also found that it's the way we say things- not what we say.

I agree here. When you feel someone is inexperienced or just no thinking then by all means speak up.

I know that if I had been the one at the counter buying the fabric I would have greatly appreciated your input. It would have saved me time & money.

Yup, I would have had to say something. Maybe, "Oh, it is nice to see a young gal like you doing your own sewing. Do you mind if I ask what pattern you are using?" If she was uncertain about herself, that would have probably been enough to get the ball rolling.

Always say something no matter what
Just take the blow if it was not wanted cause its over in a few
but at least you did your good deed
and may have saved both the cutter and the woman at the same time

Oh my, I am the same way. Also I think I should mind my own , but cannot help myself. Just think of the poor lady who will get home and be discouraged with her project right from the beginning. That kind of thing makes UFO's!

I think it would have depended on how the girl asked for the yardage. If it sounded like a question mark at the end, I probably would have piped up. But if she seemed like she knew what she was doing, I've found it better just to keep my opinions to myself.