The short answer is "Absolutely not!"
First, firms generally understand that candidates are interviewing at multiple firms during the lateral job-search process. Thus, firms understand that a candidate may have to see the interview process through to completion before giving an answer on an offer.
Now, having said this, it is equally important to keep in mind that the firm with whom you are interviewing is likely considering other candidates as well. In order to be fair to all parties involved, while you do not have to give an answer on the spot, you should not let an offer sit for so long that you prejudicing the firm's ability to consider other candidates. Absent extraordinary circumstances, you should respond to the firm's offer within two weeks of the date you receive the offer.
This brings up another point about offers made on the spot. A verbal offer is fantastic, and you should definitely let the firm know that you are enthusiastic about the offer. However, it is also important to take the opportunity to review all the important terms of the offer in writing.
For example, will the firm prorate your hourly requirement based on the time of year that you are joining? If you are relocating, will the firm pay for relocation expenses? What does the firm offer in terms of medical and other non-salary benefits? These are all important considerations that can have an impact on your decision. Therefore, while it may be tempting to give an immediate response when you are thrilled to receive an offer, it is crucial that you understand all of the terms of the offer before making a decision.
Finally, consider the huge importance of the decision you are about to make. There are many factors that can make an "on-the-spot" offer enticing. For example, in tight markets it may be hard to imagine that you'd turn an offer down. But even if you are thrilled and maybe even consider yourself lucky to have received an offer, it is still a hugely important decision that should not be made in haste.
Taking time to think about an offer is perfectly understandable, and in most cases it is expected. As long as you convey enthusiasm and thank the law firm for the opportunity to consider their offer, you should not think twice about asking for time to give careful consideration to this very important decision.
One final word: just as there is not a "rule" that obligates you to accept on the spot, there is also not a "rule" that precludes you from doing so. If during the interview process you feel that all of your questions have been answered and you know the terms of the offer, there is certainly not a "rule" against accepting it on the spot. In my experience, I have found that once the excitement over receiving an offer calms, people almost always have some questions that need to be answered before a decision is made. Thus, my general advice is to give yourself the opportunity to identify and ask those questions before giving an answer.
In conclusion, if you receive an offer on the spot, you have obviously made a tremendous impression on the firm. Don't be afraid to take time to think about the offer, especially if you have any questions that you would like to have answered before making a decision. After all, no one is going to blame you for taking the time to give serious consideration to such an important decision.
See the following articles for more information:
- Playing With Fire: Using a New Offer From a Competing Firm as Leverage to Get What you Want at Your Current Firm
- Should I Accept My Firm’s Counteroffer?
- Should I Accept My Current Employer’s Counteroffer?
- The Danger of Counteroffers