I knew someone a while ago that had had a house For Sale for some time but had had no offers
Then they got a knock on the door from someone who had viewed
they were asking why their offer had been turned down and wanted to talk directly to try to sort something out
The sellers had not heard of the offer
Naturally they went round to the Estate Agent's and demanded to know why they had not been told - they were told that the offer was too low and so they didn;t want to bother them with it
which is, as has been said, illegal
but their profits depend on getting a good price so - sometimes they might be tempted!!
In this case they were actually desperate to sell as they needed to move for work so they had made it clear that they would consider any offer
but as that would affect the amount the EA got then they thought their interests came first