decline the offer letter after accepting it

Hey Everyone, so I am in this situation, where I have an offer from GDIT as an intern, but also waiting for Booz and Splunk for their response too. What I am planning to do is accept GD's offer, and if I get Splunk or Booz, I will decline it later, and I do have a couple of questions about that:

• Is GDIT going to flag me from future employment (10+ years from today), if yes then how they will flag me, by ssn or email or?
• If I have to decline it after accepting, how should I do it?

usa jobs
usa jobs resume
usa hotel jobs
usajobs
usa jobs federal government
usa job in ksa
usa jobs
usa jobs login
usa jobs gov
usajobs.gov
www.usajobs.gov
usajobs.com
usajobs
usajobs.gov official