[mmavnn]

Yes. Be polite, have an accurate view of what your time is worth and be open about what you're asking and why.

People may not want (or have the authority) to change the deal, but if they are offended by you asking you do not want to work with them. It implies they are looking for a drone, not a real human being.

I've worked in several local government jobs in the UK, where budget (and 'Single Status payscale') constraints mean that the hiring manager normally doesn't have the authority to change the salary offered. Just asking the question has still given me an invaluable insight into the manager's way of thinking.