"He sells glasses of coffee."
Translation:Anh ấy bán những ly cà phê.
(2 years later!): Absolutely, yes.
Btw here is the direct object glass(es) = (những) ly, and not coffee, the latter beeing descriptive of what is inside the glasses (of coffee). In such case my old guess that coffee is uncountable doesn't matter.
In my opinion, he sells glasses of coffee can be expressed with những or without (my preference), knowing that if our man would sell a glass of coffee only, the vietnamese sentence had been anh ấy bán một lý cà phê for sure.