When looking for jeans at the thrift store I only focus on the style I want and finding the right waist size because I am short I can ALWAYS hem them.
Here is the easiest way to hem dungarees while keeping the original hem.
Measure and cut off the amount of material that you wish to shorten the pants by. See with swath in the above picture for reference. This should be one cut across the whole pant leg so that the piece you are removing is still an intact ring of fabric.
For the second cut leave a centimeter of material still attached to the original hem and cut off the excess. You will then have a ring of denim and another small ring of about a centimeter of denim with the original hem attached. Put the ring of denim aside and keep for patches or scrap.
Slide the original hem piece over the pant leg right sides together (this means putting the two nice exterior pieces of fabric together). The hem should slide on first so that the two cut edges line up. Make sure you line up the side seams too!
On the centimeter of fabric you left above the hem, place the foot of the sewing machine and sew all the way around or begin sewing by hand just above the original hem.
Once the two pieces of fabric are sewn together fold the hem piece down into place and iron.
Repeat this process on the second pant leg.
You now should have shorter pants with the original finished look!
The pant leg in the picture above shows the finished product after ironing. I hope this makes life a wee bit easier and your pants fit a lot better!