I think some wind up measuring across the handles, so I usually ask them something like: "what is the dimension across from one end of the bowl to the opposite end of the bowl without including the handles?"
One guy have me told me 30 inches, so I explained the different sizes & he came back that it was a 26. The pic didn't show the triangle & it was a MBH, so I went to look at it. It was a 22 & he sheepishly said that he was guessing because he didn't have a tape measure.