I thoroughly enjoyed my time bargaining when I visited Ecuador. I think I would have loved it even more if I spoke Spanish :).
However I have a few qualms with this.
1. Most shoppers on the internet are using the internet for three reasons; (A) they are looking for the lowest price possible, (B) they are minimizing their shopping time, or (C) they are looking for something they can't find locally at a brick and mortar. If I were an (A) or (B) shopper, this is a huge turn-off to me. It is neither explicitly giving me the lowest price possible nor is it time efficient.
It might work with the (C) shoppers but that that would require some testing. Do you think a Fab.com or Etsy retailers would use this? [Not being snaky, an actual question]
2. The emotion of bargaining does not translate with e-commerce. To me, e-commerce has always been an emotionless experience.
Whenever I was buying something in Ecuador there was a certain rush I got when I locked horns with a merchant. We developed a certain bond when we finally came to an agreement and each party has thought they had won. That rush is missing here (for me anyway). I'd be curious to hear how merchants feel who normally do business this way.