Ok namedchanged, another way is looking at the maths of it all. You never own the house until the mortgage is paid off and assuming the OP is using a mortgage lets look at the figures of an asking price purchase compared to a cheeky offer that is accepted.
Asking Price £350,000
Deposit £50,000
Mortgage 3% 25 years £300,000
Stamp Duty £7,500
Total Cost over 25 years £434,290
Reduced Sale Price of £290,000
Deposit £50,000
Mortgage 3% 25 years £240,000
Stamp Duty £4500
Total Cost over 25 years £345, 932
So by negotiating a discount we have saved £88,000 over the lifetime of the mortgage. For me that means we could retire at around 64 not 68 or that would help fund both our children through University. I certainly don't lie awake thinking if I upset a total stranger by offering an insulting opening bid to someone who I met once and will never meet again.
Obviously the OP's budget is much larger so much larger savings to be had on any mortaged purchase.
I was told from an early age you always make the money when you buy something not when you sell it. Offering asking or close to it in this uncertain market would be crazy imho.