It is easier to point out problems than to solve them. Avoid using extreme positions that lead to a yes or no answer, unless of course you mean it. It is difficult, if not embarrassing, to reverse yourself later. The employer would gain greater appreciation of why you are saying what you are saying. They may or may not be able to meet your expectations, but at least they would understand better your reasons.
Negotiation is nothing but give and take on both sides.
Both sides must feel that while they might have given up parts of some things, they have gained on others. Avoid a Yes or No answer on the spot, unless you are absolutely confident of your answers. No matter how hurried you or the employer is, both can wait for the right final answer for a day or two, if not longer. Sleep over your decision, before announcing it. In-person negotiations are inevitably more personal and can confine you from being more open and rational.