Now a days I am watching a common tendency of most of the clients that they post jobs for hourly contract but when they call for interview they offer fixed price job. It also fixed price jobs are offerd at the lowest cost. It makes the freelancers unsatisfied for oDesk freelance marketplace. We all community members should request to odesk so that they prevent this such cheating and make keep us on work flow. Even I am also facing this problems.
I think you shoud not let clients dictate the project terms. If you are not satisfied with what the client is offering , then be cear about it and say no. I do not think odesk will interfere with the negotiaions between clients and freelancers. Clients will always want to offer you a lower price but you must learn to be firm about your terms because once you accept, it is up to you to deliver on them. Never accept any unfair terms.
I've noticed them doing that too. I wish people would just be straightforward in their job description. Anyway, I usually withdraw my application if clients start getting unreasonable.
Another thing to consider doing is flagging the ad: It's in the wrong category. Same is true for clients that post hourly Entry Level ads that have a description that clearly puts them into the Expert Level category.