First of all, sellers who are insulted by any offer in this changed market are not well prepared by their agent. No seller should be expecting a full priced offer. All offers should be seen as a starting point for negotiations. Buyers do not want to start too high as they are concerned with overpaying for a home. Any offer should be viewed as a starting point.
That said, I am going to assume that you are working with a buyer's agent and not in a dual agency with the seller's agent writing up the offer. In this case, you should ask your agent to do a market analysis of the homes recently sold in the area to back up the lower offer. It might not prevent the seller from considering the offer low, but it can justify it.
If you are in a dual agency, your agent cannot do a market analysis for you as he/she cannot do anything to harm either client. What I would suggest in this case is to find the homes you believe have sold for less and give to your agent to present with the offer.
Here's a link to a post on my blog about lowball offers: http://mnrealestateupdate.blogspot.com/2008/04/lowball-offer
If you are looking for a realtor to assist you in your purchase feel free to give me a call. 612-239-4858.