Is it true that back in the day farmers would whiten a horses teeth to make them look younger?

I heard that sometimes farmers would whiten the teeth of an old horse to make him look younger so they could sell him for a much better price, as though they were selling a younger horse. Is that actually true?

Is it true that back in the day farmers would whiten a horses teeth to make them look younger?
I wouldn't be surprised. There used to be Horse Traders that did all kinds of tricks to help sell their horses. Kind of like used car salesmen.