Some hosts consider it offensive when guests want to negotiate on the price, or when they ask for a discount, and will decline the guest on that basis alone. Many hosts consider it a "red flag" or sign of concern when a guest seeks to bargain about pricing. THis is more likely to be true if the host has already stated in their listing that their prices are firm and no additional discounts will be given(which some have taken to doing, because they have had so many guests trying to bargain) . Keep in mind, that when a host sets a weekly rate, or monthly rate, or lower seasonal rate (eg lower rates for winter) those are already discounted rates. I have experienced numerous instances of guests asking for a discount on an already quite discounted rate. This can be annoying, as it suggests that the guest does not understand the system, and does not understand that the rates they are seeing are already discounted.
Another thing to keep in mind, is any particular hosts' rates, and how those compare to rates of other hosts in their area. A very common complaint from hosts, is that guests are going to the listings that are already the lowest priced listings in that area, and asking for more discounts on those already bargain places. Hosts can be offended by this "lowballing" and feel that the guest is not showing respect for the host's generosity in having already extended lower rates. Some guests dont' understand the cost of housing in certain areas, and I have heard of many cases where hosts have been asked by the guest to provide a 50% discount. Guests who do this will almost certainly be turned away and considered unreasonable.
On the other hand, there are hosts, and @Anand-And-Chef-Mason-Gre0 are indicating they are among them, who are open to negotiation on prices with a prospective guest. But in my experience, having had many discussions with hosts about this, hosts who are open to bargaining on prices are more the exception than the rule.
My advice would be -- if you want to negotiate on the price, ask once, politely. ( THe more politely and succinctly a guest inquires about this, the more likely the host will respond in kind) If the host indicates the prices are firm, drop the issue, and do not push or argue on the matter, as host is not likely to appreciate a pushy guest.