Doomsday

A puppy! 

... Maybe I should actually close threads when I say they're closed!

...

Are you for real?

I feel like xeno has somehow decided my side for me. 

http://www.youtube.com/watch?v=FGK8IC-bGnU

1: Define "objective value."
2: Compare it with the analysis in your first paragraph, and tell me what the difference between the two is.

You offer interest!  Depositing 100 apples now to withdraw 102 apples later isn't bad!

Oh, I'm definitely not talking about the fiduciary duty issue in the context of the scenario where people are deciding for themselves the offers they will make.  At that point, you're pretty much a giant Craigslist, so w/e.

However, the automated system would absolutely still be a fiduciary duty.  You don't get a right to neglect the duty to a client just because you've automated the process of negotiation.  If a real estate agent handled all deals by setting up a computer program which read online house listings and threw out offers, the real estate agent would still be the person deciding to use the program, deciding the parameters of weighing valuations for aspects of properties, etc.  You don't get to avoid fiduciary duties to clients just because you surrender the very power which you're given.

But even dropping the legal issue, there's the practical issue I mentioned.  Very simple scenario:
George wants to sell a house.  He's looking for items of value equal to $200,000.  (I'm using currency here just because it's easier than saying "1 million pop tarts")
John is willing to buy that house.  He's willing to pay total items worth $400,000 for that house.

A deal will inevitably go through.  No doubt.  However, the sole question is where the price will be set between $200,000 and $400,000.  Either person could hire a real estate agent who would negotiate to get what's best for them (In George's case, selling that home for $400,000.  In John's case, buying the home for $200,000).  Or they could roll the dice and go with your abstract algorithm.  No matter what deal is set up in the system, to at least one (if not both) parties, the deal would have been worse than what was very feasible.  Quite frankly, that algorithm is just a bad representative for the interests of both parties, and they would most likely look to hire real negotiators.

Oh, also, don't forget that this system is violating core principles of fiduciary duty to clients.

Real estate agents, attorneys, and other individuals representing people in business transactions generally have legal duties to prevent conflict of interests.  In particular, they generally cannot represent two individuals who are in an inherently adversarial transaction.

For example, if I'm selling a high-class house for $1 million on behalf of a seller I represent, and a buyer I also represent looks at the house and tells me he'd be willing to buy it for as much as $2 million... what do I do?  Do I get the transaction done at $1.5 million and split the benefit between them both?  Prefer my buyer and get the $1 million offer?  Or go to the seller and suggest he re-list his property for $2 million and enjoy the nice extra benefit?  The problem is that, due to my fiduciary duty, both the buyer and seller were expecting me to do what is in their best interests.  However, I'm in a situation where it's impossible for me to do anything without violating the best interest of one party or the other due to the negotiating wiggle room.

In this case, people are giving XenoCorp the authority to take their property and engage in transactions with other customers of XenoCorp, going so far as to take the individual out of the price negotiation.  The problem is that XenoCorp represents both the buyers and sellers in the deal, and will have vested interests on behalf of both parties.  As a result, XenoCorp would either:
A: Not give each person it represents the best deal they can possibly get, in which case they're a shoddy representative, and/or:
B: Outright screw over one party

It doesn't matter if it's an optional thing for clients.  The fact that you offer the opportunity to engage in the conflict of interests is inherently bad because they're supposed to trust you, and you're placing yourself in a situation where you aren't to be trusted as their representative.

And before you ask, the thing which differentiates XenoCorp from the business you linked to in terms of fiduciary duty is that XenoCorp is proactively negotiating price on behalf of the original owner.  The company you linked to, in contrast, is basically acting like Craigslist.

Btw, +1 TPs for xeno and Yell for actually having an interesting debate here.