Use the estate agent, as they will know what the sellers mindset is. We viewed a load of houses when we were buying ours including the one we bought even though it was on at £350,000, £30,000 over our budget and when they asked what we thought we told them straight our budget was £320,000 they approached the buyer and deal done.
In the end they don't always give a shit as long as they sell and move on to the next one.
Possibly could have got more off but saved all the crap