[Twistofsin]

There's really not enough information in any of your scenarios to make a good ruling. Generally if the guy doesn't look like he's shooting an angle you must cover his entire all-in unless the dealer confirmed the amount first. "About" isn't a value. It's like penalizing a player for revealing information when someone at the table asks him what he has and he responds with "A good hand."

If someone goes all in before you simply ask the dealer "How much is it to call?" I would never expect to pay anything less then the actual amount he bet unless the dealer miscounted the bet and told me the wrong amount after I requested a count.