If I'm offered a job position can i ask to think about it? does that look bad?

It doesn’t look bad to ask for a few days to consider a job offer. If you should be offered a position on the spot, you thank them and then tell them you need a few days to consider, and would be happy to get a response to them within three days of receipt of the written job offer. In my experience, most written job offers (which you should expect anyway so you know exactly what you are being offered for pay and position) include a timeline for response, ranging from 3-7 days. What is not okay is to continue to ask for more time while you wait to hear back from another place. If you initially ask for a few days, then at the end of that time you need to give them your answer. If you think three of your interviews went well and are waiting to hear back from two of them when you need to give the first one the answer, then you either decide to accept the job or reject it and continue to wait to hear on the others, but you don’t ask for more time.

(Generally speaking, being offered a job on the spot is more often a red flag than not, because it can indicate that the company is desperate to hire people.  Not always, but often.)

FWIW, there are very few jobs that would require you to accept it on the spot.

Tell them you'd like to think over all the options they are offering and conduct an Economic Analysis comparing the position you are in now and their offer.

They will think that you are conscientious and thorough in your decision making process.