The combo I am always looking for is Money + Project
(by “Project” I mean the technologies I am working with. It has to be something popular, from the latest dev. stack and also very important as well, are the people I am working with, they have to be experienced so I can learn something form them).
Both Money and Project are equally important, although I would definitely take a job paid less if Project is better.
It’s a choice which on longer term should be much better.
On the other hand, in times when I was paid very low, I switched jobs even if the Project was somehow the same or didn’t seem way better than I was doing.
Even if existing work place and conditions are great, this never counts to me as long as the Money + Project combo is not right.
Now, regarding your position:
If offer is really 2X more money, you are either earning very low OR there’s a catch.
If you think there’s a catch, you need to make sure you ask all the questions you can to try understand exactly what are you getting into.
For example, you could ask:
“if you’re going to hire me, what exactly will I be working on. What kind of tasks will I be working on?”.
You could continue and add to the question some very practical examples based on what they told you, like (suppose it’s mobile app development) “Will I be working on implementing the screens with technology X? Do you use framework Y?”
If the person is not technical, ask to speak to someone who is, maybe the person which you will be working with each day.
Getting to know a little the exact people you will be working with day by day is very very important, it’s equally important as the money and project.
In my experience, I went to interviews meeting with managers which had no fucking clue what I will be doing exactly.