Dual agency for a lower price: yay or nay?

[Patricia J.]

I am in the process of purchasing a condo as investment, and it occurred to me I may get a deal on the purchase price if I ask the listing agent to represent me as the buyer as well. I thought the agent, in wanting to get both sides' commission, would try to make the deal work even if my offer price is lower than the market price. 

Has anybody tried this? Am I mistaken in my reasoning? I have purchased properties before and am fairly familiar with the documents and purchasing process myself. 

Thank you!