@Snugglemonkey
''We are currently selling. I would consider 25% less an affront and there is no way I would sell to you at all, even if you made a better offer subsequently..''
As people have commented already this is a business transaction for the buyer. It has nothing to do with how you feel about the property and it is not about making sure you don't feel offended...
Of course the buyer is going to look at a property and make their own assessment as to how much they would pay for it, based on the condition, location and so on.
Buyers who are not in a chain or don't need a huge mortgage also realise they are in a better position and will expect to get a better deal for it because the sale is less like to fail and will complete much faster.
Many estate agents tend to over-value homes to get the property on their books and sellers will try to get as much as they can from the transaction. it is perfectly normal for a buyer to offer a more realistic price.
You don't have to accept an offer but equally buyers can choose to offer what they think your house is worth and move on to another property if it is not accepted.
As I mentioned above I saw a house at £250,000 last week and was considering an offer at £240,000. The agent emailed even before I had a chance to do that to say it was now reduced to £225,000. The initial valuation was way too optimistic and there is no way I was going to pay £250,000 for it because the house, although lovely, needs updating, including a new bathroom.