dual agency?

Ok, I have a question for all the agents out there, but first let me give you some background.  I was presented the other day with a unique situation where a woman came to one of my open houses, stated to me very clearly that she loved the home and had cash to purchase it, and said she would be back to write an offer. I thought to myself, wow, very cool, the home's first open house and already a cash offer! Pretty good. The woman came back and subsequently asked me to help her write the offer. I asked if she was working with an agent, and she stated no she was not, but wanted me to help her. I told her that I can most certainly help you with the paperwork to write the offer, but I cannot advise you or help you with negotiations because I represented the seller. She then asked me if I could just represent both of them in the capacity of a dual agent. Now, I know you can do this in certain situations with written permission from both the buyer and seller, but I was not comfortable at all with this set up, so I called a colleague and got her represented. My question is... have any of you out there ever been in a similar situation, and what are your overall thoughts on dual representation? Thanks in advance for any feedback you might give. Very much appreciated.