It really comes down to the motivation of the seller. If motivated, they'll happily drop the price fast if they feel you're about to walk.
Just happened to us.
Under contract. Found out repairs were what I estimated, but we miscalculated the ARV pretty bad. (it was a rushed offer, unfortunately).
Rather than "negotiate", all we did? We had our realtor drop hints to the seller's realtor:
3 days before DD deadline: "Oh, they had an estimate come in that was way more than they thought. Not looking good. He's going to get another estimate, don't worry."
2 days before DD deadline: "Hmm, the layout in the kitchen is going to be tough to resell. They may have to knock some walls down. Will keep you posted."
1 Day before DD deadline: SELLER'S AGENT: "Look, my clients don't want to go through this charade again, can we drop the price $20k and call it a deal."
We didn't even need to negotiate.
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In the end, we walked anyway as we bought the house sight-unseen and the layout was freakin terrible and unfixable. But, we probably could've got them down $30k.
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As someone fairly new at REI, I always assumed "as is" was no repairs NOT "you pay and leave it at that." If you insult the seller's by renegotiating...who cares? I feel like 90% of this business is rejection, should be used to it by now :)
NOTE: It was not our intention to renegotiate the price down. We didn't offer them a good deal with plans to renegotiate later as that's unethical. So this isn't a tactic for every deal. We simply opened the front door, saw the layout and went "No, no, no!" This was not pre-planned.
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More reasons for why I believe you can renegotiate AS IS:
In negotiations right now for another house. "AS IS" purchase. Put in offer with only seeing pictures. Walked through house after they countered. Saw we needed $25k more repairs than I thought due to smaller-than-it-looked kitchen and misleading-picture-size master bath.
Wrote up a note to sellers listing what it'll cost us to get the house up to the level of the neighborhood. They dropped $15k off their price in 24 hours. (Yes, this wasn't a binding contract, but offer is still 'as is')