I am not going to argue categorically whether you should or should not consider a counter offer.
But I think that if you get a counter-offer, your response ought to be something along the lines of "Gee, that's a very flattering offer. May I havea day or two to think it over? By the way, would you be willing to give me a memo outlining the offer so I can be sure I understand this offer completely and correctly?"
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