Misrepresented Square Footage - Concession Request

[Brad Jacobson]

Hi Fellow BP Fans,

I'm currently UC on a triplex that I snagged off the MLS last week. It was a competitive bidding war.

The MLS listing noted the combined square footage of the three units was 3,600sf. During the walkthrough, I felt like 3,600sf might be a stretch but I still fought to win the property. The seller's property condition disclosure notes that the square footage was pulled from county records but upon my personal review of county records, the property only measures about 2,800sf.

I contacted the listing agent over this and got no response. A few days later, the MLS listing square footage was updated (after it was noted under contract) but I still received no feedback from the listing agent. Luckily, I had saved a PDF of the prior measurements.

My partner and I decided we're going to use this as a due diligence finding and therefore concession request to try and knock down the price since I had to compete with several other parties for a largely misrepresented property.  

My question is - what is the most effective way you've done or seen to get a large concession when purchasing a home?  It's one thing to ask for a new water heater, it's another to ask for $30,000 off for a misrepresentation.  Any hot tips on knocking down a sales price significantly aside from simply explaining why and asking for it?  What have you found to be the most effective negotiation technique when talking larger numbers?

Thanks in advance,