In that case they should ASK for clarification. Unfortunately, too many bartenders -- even good ones -- won't, they'll just make what most patrons seem to like. This is sadly true even at fairly high-end restaurants and bars.I also must say, having tended bar myself, that I didn't care to be told how to make a drink by a customer. It's only fair to tell a bartender if you want the drink to include this or that, if that ingredient is out of the ordinary. But if you want a perfect Manhattan up, ask for that. If the bartender literally does not know what those words mean...
I like a "standard" martini, dirty and "up" -- with a 5 or 6:1 ratio of gin to vermouth. Sadly bartenders seem to think that a Standard Martini is a cold glass of gin or vodka. They have no idea anymore that Martinis: a) should be gin, unless otherwise specified, b) should contain vermouth, and c) should contain at least 3 olives.
I've tried ordering "standard" martinis, a "dirty martini, medium dry" and various other ways. Still often ends up as a cold glass of gin. I even had a bartender at a particular well-known and well-regarded "Martini Bar" tell me she wasn't sure they HAD any vermouth.
Needless to say, I rarely order a Martini when I'm out anymore.