I was offered a job at a company, and I only have one week to respond. The offer is good, the company is good, but I'm not completely certain about it. I am looking at different companies. What is the best way to delay the offer until I find a company that I am certain I want to work at?
I don't think I can do better than link to Joel Spolsky's article: "Exploding offer season". While aimed at new graduates, it explains exactly how this works and how you should respond.
Occasionally companies are really looking to find someone to start in a couple of weeks - but it is very, very rare that they would rather have someone now than wait a week and get someone good. They will almost always give you a week or two to make up your mind. Remember that 'considering other offers' makes you look good in their eyes, not bad. However it's important that they don't think you are playing games with them. Give them a deadline by which you will get back to them, and stick to it.
If they say they absolutely must have an answer now, then that's like a car salesman who says the offer is only valid 'right now'. You shouldn't take it. The only reason they would want to stop you considering other offers is if they think the other offers would be better than theirs.
I think breaking this post down may be helpful. Being decisive in a job search is usually a function of being prepared and having your expectations properly set before starting the search. I usually advise candidates to try and have a very clear picture of what job they want, so when they find it they will know.
One week is a fairly reasonable amount of time to provide for an answer (in case you were wondering).
What are you not certain about? You say both offer and company are good, so you need to decide what exactly you are waiting for in the job search. Of course something better could always come around, but will it? Some candidates do not want to take the first job offer given (using the 'don't buy the first car you test drive' theory), but what if that offer is indeed the best?
Delaying this offer gives you the risk of losing this offer. The old 'bird in the hand' cliche. If you are willing to risk losing the offer, tell the company that you are still in your job search and assessing other offers. They may ask 'is there anything we can do to expedite your decision?', which generally means 'how much more money do you want'? If it's a money issue and they ask you that, I'd tell them 'if you up the offer to $X I will start on mm/dd'.
Your success in talks with this company and others that make offers is very closely tied to demand for your skills. If you are a highly coveted professional with a rare skill set that is in high demand, you can expect companies to allow you to delay your decision (at your own potential peril, as they will surely continue interviewing other candidates). If your skills are relatively common, your request to delay an answer will not be honored.
Companies generally will not take kindly to candidates that they feel are using their offer and shopping it to other companies to try and start a bidding war. If your skills are rare, you may have some success with this tactic (I'm not saying that is what you are doing), but it can often backfire.
If you like the current offer and company, I think the first step is to ask yourself 'what would another offer have to look like for me to turn this existing offer down'? If you can picture what that other offer would be, and you feel you have a reasonable expectation of finding that ideal position, you probably shouldn't accept this offer under any circumstances (unless you just really need a paycheck).
You really need to ask them for more time to consider their offer so you can $(FILL_IN_FROM_BELOW).
Make sure you have a reason which makes sense - some good and valid reasons are to:
You really don't want to give the impression that you are not seriously considering their offer because you are waiting for other offers.
If you have only one week, you could phrase your request, "is it possible I could get back to you by $(DATE_IN_FUTURE), I have to $(FILL_IN_FROM_ABOVE) first and I'm not sure one week is enough time to do so?"
And whatever you do, don't lie about your reasons.