Wylie if you re-read the posts you would see that I wish to buy his share out. The original question was because he got a dodgy valuation as he wants a far higher price than it is worth and I was querying what I could do about the valuation. It's so misrepresentative I thought it was probably illegal and I have received advice about that in the posts above (apparently valuers can get away with anything).
The only way he might get to accept what it is worth (far from his valuation) is auction. With all the associated costs. There are no more costs except some agencies will charge you $500 for the auctioneer. Some don't charge anything. You don't have to pay for any advertising other than on re.com or Domain, but you could be best served to suggest that you only list it on the agency site, which will mean much less traffic to see it. I don't want to pay for his ignorance and petty bullying behaviour. Hence not wanting to go to auction but seeing it as the best case scenario in an unfortunate case where he may not mind spending dollars on lawyers and agents but I do.
It seems he has already sought out a lawyer, so I doubt he will see "sense". He thinks it is worth a lot, you know it is not worth his valuation. You aren't on good terms. He isn't going to back down. I see the only way to get out of being tied to him is to sell or auction. Selling means choosing a price, which clearly isn't going to happen.
You could start at his inflated price, and let it go stale, but even if you buy his half once the market shows it is listed way too high, he is still never going to accept that what you offer is fair to him.
I see no other way than to auction it. Pick an agency with no extra cost, or pick one and pay the $500. That is all the extra an auction costs, and if you pick an agency that doesn't charge anything for the actual auction, it doesn't cost one cent more than a private treaty sale. There should be no legal fees and there will be commission on the sale which wouldn't be a cost if you could buy him out... but that isn't going to happen, so I reckon you make the best of it and auction it.
I'm about to send his lawyer my valuation (received before his inflated one) and see if he can see sense. Other than that, I am going to wait it out. Terry agreed this is a good option.