Last time I was looking for a job I ended up with offers from both places I was interviewing at. I renegotiated and signed one of the offer letters.
When I called the other company, they asked me to sign with them even though I'd already signed a different offer. Because this is tech and people do it all the time.
It just felt dirty. I had already made my choice, and would not have changed my mind. But I've got an older mentality where it feels like I am burning bridges if I reneg after signing an offer.