From 60-75% of the candidates who ask for more money, get it.  So, if you don’t ask, you will always wonder if you could have increased your salary from the start.  You can either have a number in mind, for instance:  I was hoping for closer to $55,000 versus $49,000.  What can you do to potentially help bridge the gap?” Or, you can ask them in general what they can do in offering more money, or, you can accept what they offer, no questions ask.  

Many times, they will give you more.  Even if it is only $1,000 a year more, that is an increase the appreciates over time through the potential raises, bonuses, and commission, which are often based on a percentage of your salary.  I have never heard of someone being told their job offer was rescinded just by asking if there was the potential for additional salary.