1) There is no easy way for a company to come back to you after you fail to negotiate and say, "I know we offered you $50,000 for this position, but we were prepared to give you $53,000. Do you want that amount?"
2) After you are an employee, you will fall into a matrix of possible raises, and that matrix contains all small numbers! If you meet expectations, you might get a 1-2% annual increase in base pay. If you exceed expectations, you might get a 2-3% annual increase in base pay. Wow! A whole 1% more than your peer who never worked late, never came in on the weekends, and never came close to producing the value that you provided to the company. It may not be fair, but that is practice that the majority of corporations follow.
3) Prove your value. Do research to show the average wage for your skill set, then demonstrate to them that you are above average and ask for more. Believe me, if they are making you an offer, they think you are well above average! Just reiterate it to them.
Before you accept the role is the only time you will have this much power in determining your total compensation. I know all of you are aware of the time value of money. If you negotiate for that extra $3,000 now, it turns into more than triple that amount over your career.
Don't worry about what the employer will think about you bringing up a negotiation, or worry that they will revoke the offer, or fear that they will think less of you. In fact, if I were hiring someone in Business Development / Sales, and they did not negotiate with me, I would have some serious reservations about keeping that offer on the table!