salary

How much of a salary increase can you ask for when applying for a new job?

As mentioned in title: 5 years of relevant working experience, all in private education sector. Currently getting pay of $3.1K, plus handphone allowance of $80. Applying for govt-related/public sector jobs, asking for $3.5K. I am willing to negotiate down to $3.3K. Employment agency ask me to lower my salary. Not sure whether can trust or not... think maybe they are in hurry to get commission. I already went for 5 interviews and have received one job offer so far but the renumeration package can't be confirmed... been waiting for 3 weeks liao