Bests & Worsts Reviews from Amazon

I thought I was purchasing the 20 oz. shaker, but I noticed how small it was when I got it. The shaker says 12 oz. on it. The picture also shows 12 oz., but's it's advertised as a 20 oz. bottle. The other pictures are not accurate either. Some people were saying if I filled it to the top it's 20. Not true. If it's a 20 oz. shaker it should say 20 oz. on the bottle. A 2 cup measuring cup says 2 cups on it. What's the difference? I've tried twice and both times I was sent a 12 oz. shaker.