What is a gift horse and why on Earth shouldn't we look it in the mouth?

Why, Jerry, that's a great question and thanks for asking. Yes, I indeed asked this question of myself this morning after using the phrase "I don't want to look a gift horse in the mouth" in a sentence today. I think I figured this one out on my own in short order, but there may be those out there who are not familiar with the nefarious ways of the horse-trader. While science,  savvy veterinarians and the Internet may have forced the horse-trader and his ilk to straighten up and fly right over the years, there is still something shifty that seems to taint the air around those in the business. I am nearly certain they prefer to be known as horse-merchants or equine distributors or some such like-term that puts much-needed distance between themselves as respectable business-people and the horse traders of the wild west, where this old saw probably reached the apex of its popularity.

In the days when the horse was the primary means of transportation, the horse trader was the equivalent of today's used-car salesman and not above misrepresenting his product in an attempt to pry an extra hard-earned shekel out of the pockets of his prospective clients. This would sometimes result in the unsavory trader being shot, stabbed or lynched by disgruntled customers. It was the way of the west and an occupational hazard.

Unsavory horse traders were sometimes shot, stabbed or lynched by disgruntled customers.

One of the means by which the shady trader would try to bamboozle his clients would be by lying about a horse's age. This little fib might lead one to believe that a horse had suffered many less miles afoot and therefore be much heartier and robust. One way to check the trader's claim would be by examining the horse's teeth, which would show wear and tear and gum damage and other red flags apparent to those in the know on such matters. This little fib might also lead to the trader being shot, stabbed or lynched. It was the old-west version of the modern-day "kicking the tires", only with the possibility of gunplay.

So, if one were so lucky as to receive a horse as a gift (the "gift horse"), it would seem unappreciative to examine the beast's teeth in front of the gift-giver. I am not certain, but I imagine seeming unappreciative upon receiving a gift horse might also lead to the eventual shooting, stabbing or lynching of an unappreciative son of a bitch.

In other words, appreciate your gifts - it's never too late for a necktie party for the unscrupulous or unappreciative.

Good day, sir.