I always wondered the meaning of this phrase, until I stumbled across this thread. That knowledge is nice, but the saying itself is now pretty antiquated.
Responses for modern equivalents?
English Language & Usage Stack Exchange is a question and answer site for linguists, etymologists, and serious English language enthusiasts. It only takes a minute to sign up.Sign up to join this community
“Don't look a gift horse in the mouth” synonyms?
ingratitude or to be ungrateful OED
- Want or absence of gratitude; indisposition to acknowledge or reciprocate benefits received; unthankfulness; ungratefulness.
Defeating ingratitude in our kids is largely dependent on them seeing gratitude in us. Fox News Nov 18, 2018
You could consider the more modern:
Don't look at gift's price tag (PowerThesaurus)
In the description of the expression you are giving, Urban dictionary says:
You look in a horse's mouth to determine its age and/or health. So if someone gives you a horse, and you look in it's mouth, it's like looking for a price tag. It's rude!