What offer should i make on a house i have seen?

I am looking to buy a house and have viewed some over the past few months.
I have seen one i like with an asking price of £157,000. It has been on the market for several months.
The couple selling the house are really nice and i dont want to offend them with too low an offer.
They have told me they have no mortgage outstanding on it.
With it being a three storey property and the couple being in their lates 60s i am thinking the two flights of stairs is the main reason they are selling.

It is in very good condition and doesnt require any major works doing to it, maybe a kitchen upgrade and decorating throughout.
What would be a fair and reasonable price to start negotiations at?

Read more: What offer should i make on a house i have seen?