At the point of salary discussion, any smart applicant gives subtle signals that he is not satisfied with the figure offered by just repeating it. It is a smart technique to get a higher offer. Anxious to get a positive response from you, the interviewer may offer you more. Your hesitation to say okay will make it clear that you are not overjoyed with the offer.
You have to prepare the pitch for negotiations and put your to research to use. Had you made thorough research, you would know what the range for this position and turn the negotiations to your advantage. You can even tell the interviewer that you know the range is much higher than his offer and your qualifications and experience should put you at the upper end of the range. Ultimately you may be successful in getting a reasonably better offer.
You see even if the offer is around your expectations, you won't be losing to be a little bit hesitant. You can directly say, “Your offer looks to be generous and I may accept it, but before I decide I would like to know ….” Thus you can start the discussion on the company's salary review policies and the range of growth you can expect. If you are not satisfied with the revised offer you can as well tell him that you will think over the offer and let them know the next day. If you are satisfied, accept it. This shows you will stand up to what you believe and you are a good negotiator. Many employers admire employees with such qualities and believe they would do well in defending the company in the market. The entire negotiation exercise presents you as a knowledgeable person and one among those who don't hesitate to take a firm stand. The interviewer will conclude that you stand up to what you believe in and you are a good negotiator.
If you had accepted the first offer you may think later that you could have clinched a better deal had you negotiated. Even you did not get higher that what you had been offered, you feel satisfied as you did make an effort to get a better offer.
Salary negotiation should ideally be put off till the interviewer knows you well and notices your plus points. When an interviewer ask you what would be your expectations, better you tell him that you would talk about it after you know what you are expected to do. Maybe, another employer tells you the salary the job offers and seeks your opinion; then also you tell him that you will discuss it after learning more about the job and the responsibilities. In either case you will end up with a better or reasonable offer.