I don't know that answer. It depends on what the comparable properties in the immediate area are selling for right now.
Comparable houses in the area are dropping $20-30k off the asking price at the moment. The ones we have been keeping an eye on are just not selling & are being reduced at the moment. There is also a lot to choose from although partner is in love with this place now!
If the Vendor is selling 3 properties right now, you can bet they are aware of the local values, but they may also be in a big hurry to off-load the 3 properties.
Led to believe vendor is a builder also offloading H&L so hoping is feeling a cash crunch
You could try a bluff. If it was an unconditional offer on 60 days or less for settlement, you could offer $600k and see what reaction you get.
Can't make it unconditional unfortunately.
If you have to make the offer subject to your house being sold, you don't have a lot of bargaining power on price.
but I'm gonna give it a try anyway - what have I got to loose
It reads in your post like the Vendor has now increased the asking price? This could mean the Vendor is trying out the market, and not in too big a hurry to sell, or they know that the price originally asked was too low.