Is it ethical to refuse a postdoc offer after lab visit I am a Ph.D. student, close to finishing up. I am looking for a post doc position and have been in talks with multiple professors in various universities. However, most of them want me to visit their lab for a talk or a presentation, without having directly confirmed anything. Although they sound positive about me, there is no confirmation yet. Moreover, this being a relatively early stage of my post-doc job hunt, I haven't truly made up my mind yet. 

I would like to know if it is unethical to accept reimbursement for travel and stay to these labs and subsequently refuse the offer, since obviously I can't accept all of them (if they happen to confirm me). Please share your opinion on this.
There are no ethical considerations here. They are willing to spend the money to get a look at you as well as let you look at them. Just be honest with them so that you don't seem to be leading them on. 

Thinking of it any other way would imply that a small expenditure from them would lock you in. That would be unethical. 

Good luck.