Lastly, and this is for those of you whose careers are just starting, I do not endorse lying about or concealing competing offers.
If you get a better offer after accepting another one, be proactive and call the recruiter or whomever you are working with directly. You may actually get an even sweeter offer than the original. But handling this properly and with respect for all parties will have the dual impact of showing your maturity AND leaving them with a sense of respect for you as a person. This can also result in a future offer that could come when you’re ready to make the next big move.
It’s not such a big world anymore, people are constantly connected, and they have longer memories than you think.