There's always a risk that someone will figure out how to enter multiple times or will disable the site so others can't enter. Limit entries to a finite number, such as one per day or one per e-mail address. State in the rules that you retain the right to disqualify entries from a user suspected of attempting to disrupt the sweepstakes, and that you may prosecute or seek other legal redress against anyone suspected of engaging in these acts. Yes, but avoid consideration. Many online promotions award gift certificates redeemable at a designated online store.
Some states also prohibit prizes of gift certificates with expiration dates.
Online promotions are under everincreasing regulatory scrutiny. New laws are continually added, and existing laws are subject to constant reinterpretation. Consult legal counsel as early as possible when constructing your online promotions to ensure that they are legally sound. It's better to spend time with your lawyer than to end up on a list of Disasters in Online Promotions.