Does the phrase looking a gift horse in the mouth originate from the legend of the Trojan Horse?
No - you can estimate a horse's age by looking at its teeth.
Looking a "gift horse in the mouth" would be like judging the
gift's value or appearing ungrateful. The general idea is: it may
not be ideal (like an old horse) but it was free & you can
still make good use of it & be grateful for having one at