Question - if you are a large group of professional photographers why take photos of horses who clearly show saddle/girth sweat marks? I would think clean and shiny horses with nice backgrounds would sell better.
Let's say the first photo is not shopped. It might sell well to horse loving kids and none-horse people. The vast majority of horse people will not believe that is a non-shopped photo.
If you are making photos for the horse market to purchase you might want to keep those things in mind.
It is the old willingness to prove I am not wrong should be enough to make them stop questioning me.
We take pictures of owners horses for the owner and not for general sale to the public. As you quite rightly say - a different style of shot would be required to put in. For example, a calender! These are natural shots for the owner to treasure.
Sorry you don't like them.