OK, I guess it might be worth adding my two'penny worth.
In my experience bowls like the one in Gary's question have not turned out to be Monart.
I would say that using eBay for 'sleuthing' is very much like asking the blind to take the lead
How do you know whether the seller knows their stuff? Some do, many do not.....so how then do you know you'er getting the correct attribution?
I my lmited experience of bowls like this that I've either owned, or handled, over the years I cannot remember one that turned out to be Monart. They fall into two categories, the light weight and the heavy(ier).
The lightweight have a multitude of irregular bubbles that bulge through the surface, which is not so shiney, perhaps even toward the matt with an unpolished pontil mark. Conversely, the heavier ones have a shiney surface and a polished pontil mark; the body is thicker walled, so the bubbles do not bulge to the surface in the same way. These pieces also tend to have a ridged base, sometimes even a cylindrical base with several ridges before it meets the bowl.
The bowl in question is the latter.
Neither bowls have a definitive attribution. Although, on occasion, they have been WMF, others have not been proven to be so.
I own a very large vase and a wavy bowl that I have never been able to give a positive makers name to. Therefore, my vote would be NOT Monart, and not necessarily WMF.