It's also ok to say "I really was expecting more. I looked at the average of entry-level people in the industry and this offer is below the median. [Make sure you have done your homework and this is true!] I like the company and I'd like to work for you. Can you help me understand how you arrived at this offer?" Be honest and inquisitive, never threatening or accusatory. Never say "I can't take this job at that salary." What you are trying to communicate is that you don't understand how they arrived at this lower offer, given the facts as you understand them.