What if I don't join someone for postdoc to whom I previously applied I am a PhD student in applied mathematics. I have submitted my PhD thesis and started applying for postdoc positions. Now suppose I informally email somebody and suppose he says that he has no funding currently and once he has funding he will inform me. Now, suppose at the time he has funding, I have some better option, so I don't join him. Can that create a bad impression of me to him ?
If your situation has genuinely changed—six months or a year go by and you’re working as a postdoctoral or researcher somewhere else, why would you be expected to give up your position? This seems like a very one-sided transaction and unfair to you. Might the professor hold a grudge? It’s possible, but anybody who does hold a grudge in such a scenario is thinking primarily about their own needs rather than your mutual benefit.