What should i offer?

[Dave McEvoy]

I made an offer on a vacant house and agreed to $67,500. I then tried to renegotiate to $58k as I believe the furnace needs replacement. They countered with $66k "take it or leave it" I followed by calling the county and town to see about any violations or liens. Come to find out there is a $12k tax lien for unpaid taxes since 2013. The best part if that the county is going to foreclose on 2/28. Do I go back to the seller and really lowball them knowing this? Do I even mention that I know this? Obviously a title search would show this too. I was thinking of offering $20k "take it or leave it" or you can kiss the house goodbye in a month and get nothing. Any advice is greatly appreciated.