For example let's say a selling agent is getting 6% on a house listed at $500k. If it sells at $500k he gets $30k, if it sells at $520k he gets $31k. If he were to get a $500k offer it probably isn't worth his time to put in a lot of extra effort to try to get that extra $1k, but to you that extra $19k is a lot of money. You might want to do another open house but the agent will convince you to just take the offer in hand. I think this is one of the reasons that agents use all these short deadlines and pressure tactics, it's not just to get the buyers locked in, they want to be in and out of each deal as quickly as possible so they can move on to the next deal.
Not sure how to fix that, but it is an issue to be aware of.