Agree with what SD R said. Its not hard to write it up. If I thought there was no chance of it being accepted I would share that with my client but I would also let them know that I work for them and will do everything I can to have it viewed favorably and to be accepted. Thats our job after all. We work for our clients.
There is defintely something to what SD R said about being viewed negatively going forward. If its a house you love and really want it takes some diplomacy to present a lowball but it can be overcome. You just say your clients are conservative and the offer is not a representation of how your clients feels about the home but rather how they feel about the market. Its that simple. I do it all the time.
Sometimes it works, sometimes it doesnt but you cant make an omelette if you are afraid to break an egg.!