House we are buying, some of the ceiling has come down!

[MillieMollieMandi]

We are currently buying a house, due to exchange at the end of the month. I've just had a call from the estate agent and some of the ceiling in the front reception room has come down!
In order not to slow down the chain & fix it himself, the seller has suggested a reduction in price & we fix it.
However how on earth do we figure our how much to reduce or the next steps! I just don't know what to do now.
Anyone experienced anything similar?

We have a 1920s house with lath & plaster ceilings. Not long after we bought it we started decorating and pulled some wallpaper off the sitting room ceiling and half the ceiling fell down(!) Looks like the paper was holding it up after all 😏. We had it overboarded and plastered - and the entire room skimmed. If it’s something similar it won’t cost too much too fix. Just the services of a good plasterer....