Many buyers can be very demanding, and I find in order to make it to the closing table sometimes you have to be able to make things happen that aren't in the book. And never give up.
A buyer's agent should be persistent, but not pushy. I was once told that a buyer selected me because I gave her the information she asked, but nothing more, unless I thought it was really important--and she really liked that.
Also, a buyer's agent should not be trying to make the most commission possible out of a sale. Someone once asked me, "Why should I hire you when you are trying to get me to pay the highest price for a house?" I explained that if my bread and butter was maximizing the most out of opportunities for commission, then I would not have that many opportunities for commission.
My bread and butter is to make my buyer happy enough to refer me to other buyers.