Hi there,
As the Vendors of the property have seen the hoyse they like, they may not be able to afford to lose 31k off the sale of their own house.
If you really do think this is a fair price, get the estate agent who is selling your property to write a letter supporting your low offer, and also ask them to give you some comparables (property details of houses similar to the one you wish to buy which have sold for the avaerage and fair price you want to offer)
Then, when you present your offer to the vendors, you can show clear evidence that the property is overpriced and you have looked into this.