I don't think the risk of purchasing any of the smaller breeds is very high for most of you involved in ranching.
The chance of any of you confusing a Dexter Bull or Cow (red or black) for an American Angus, Limousine, American Simmental etc, is pretty slim. Most of your replacement heifers are either taken from your own herd or purchased from reputable producers.
For those of you that like to roll the dice at the Sale Barns or on Craigslist, you may on a rare occasion wind up with something you had not planned on. When rolling the dice I believe that is what is referred to as "Snake Eyes".
Little calves do grow.