You see o.n.o. in British small ads, especially for a car, a bike, a sofa, or a flat. It stands for “or near offer” (some people read it “or nearest offer”). The seller names a price, then adds o.n.o. to say “I want about this much, but you can offer a little less and I may still say yes.” It is a polite, slightly old-fashioned classified-ad code, not a word you drop into spoken sentences. In conversation you would just say you are open to offers. American ads more often write OBO, “or best offer”, which is a bit more open: the seller may take the highest bid, not only a little under the asking price. Though actually the phrase belongs to paper notices and old listings; apps now have a button for “make an offer”, but British small ads still use o.n.o., and people still understand it. It does not mean “oh no”.

（英國售物廣告）可小議、接近此價亦可。台灣廣告比較常寫「可議」。