Tingle is annoying, yes, and demands ludicrous amounts of money. Ravio does the same except even worse. His very manerisms scream "Punch me in the face!". BUT that's only the tip of the iceberg. Consider this. Ravio knows what's going on. He knows Hyrule's doomed. He's not courageous enough to stand up for what's right, okay. But then the smart thing to do would be to go to Link, explain the situation to him, and give him all the items. But is that what Ravio does? Oh no. Instead, he says nothing. He lets Link walk right into the trap. And what's more, he makes Link pay for those items. Oncoming apocalypse? Well let's profit at other peoples' expense. Oh but let's take it a step further. Let's actively hinder his progress. Oh what's that, you found a sand rod? Technically a violation of a contract, so I'm stealing it from you, nevermind the whole end of the world thing. The fact that he knowingly sent one of the sages off with it into the Eastern Palace is also baffling. Who's side are you on buddy?
In short, he's obnoxious (moreso than Tingle, and that's enough reason alone to dislike him), lying, manipulative, cowardly, greedy, uncaring, and on top of everything, serves a freaking Deus ex Machina, lest the plot actually be resolved in an interesting or meaningful way. He's the worst kind of character imaginable, being both a bad human being and a bad plot device.