The critical thing is to confirm in writing either way you go. This can be done by mail or email. It is important to ask for time to evaluate and discuss your offer with those you trust before automatically accepting. Once you accept, it is unethical to decline if a better offer comes along unless there are compelling reasons. The employer is also expected to live up to it’s written offer that was made. The Riley Guide website collects and shares many articles on evaluating and negotiating job offeres.