I got the offer with company A about two and half weeks ago. I supposed to start on last week, but got some problems with paperworks so they delayed my first day for another week. While I was waiting for their call, I've been interviewed with a company B and got scheduled with the second interview on Monday next week. Meanwhile, just right after my interview with company B, I got a call from company A saying that they have finished and expecting me to start on Wednesday next week. Now, I have to say that I am really interested in company B and really hope that I left a good impression to recruiter and they will offer me a job. The question is that is it acceptable to turn down the the job when you have signed all paperworks and they are expecting to see me at the workplace right away? (This is not a contract job) If it is possible, then how can I do that in professional manner and without ruining the relationship with the recruiter? Also, this is not the first I am turning them down. Unfortunately, this is the second time. I really hate that I put myself in this situation. I hope, that someone on this forum can give me some advices to figure out what to do in this confusing situation. Thank you in advance.
"Oops, I'm not interested after all" is not professional. There is no way to adequately apologise for having wasted their time and money, and no way to avoid looking like a flake. You are breaking your promise.
Having said that, it sometimes happens... Just as companies sometimes discover they can't use you after all, which is equally unprofessional.
Don't do it for anything trivial. But if your dream job suddenly becomes available, you'd sorta have to jump at it.