Stan, as far as I know it doesn’t happen. It wouldn’t be proper to reveal the names of the offeror and for negotiations sake you don’t want to put out the word as to price if the offer is low.Unfortunately , some agents hide behind the reasonable expectation of privacy. The buyer’s agent should be able to give reasonable feedback as to how much sense the supposed offer makes with respect to the property and market conditions.
I think I can tell when the agent is full of beans. Like the OP, I am not usually prone to sticking around to find out but it can be a bit of a dilema. In 2003-2004 you were not going to get some of the best properties unless you played the game without knowing whether it was legit or not.(whether it was a good idea or not being another question)
For cutting to the chase, I am a big fan of the “letter of intent”. It is a one page non-binding offer to purchase at stated terms and conditions. I have at times sent as many as five of them out on properties without actually having looked at them….more if I have looked at the properties.