Have you rejected an offer after signing?

At will employment...things can go both ways after offer signing. I rejected once and they came back with a beefed up offer once; another time, I never heard from or worked with the other company.

It happens all the time. Just don’t be an ahole about it.

Yes, just make sure to have a valid reason and don’t delay telling the company, be transparent

My very first offer. I signed an offer with the company I had interned with, well before I graduated. Then I ended up getting a much better offer from another company. The first company was a very small startup barely scraping by, the second was a large, established one, so the first one understood. I'm still on good terms with them and have done some contract work for them here and there when they needed help.