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.