Lot of winners who had been selected under the American diversity visa lottery program used to lose their visas and their visa processing fees at the time of their visa interview, every year. This used to happen mainly to their ignorance of the visa rules.
Plenty of them participate in this DV Lottery program because it is a free to apply program and most of them didn't know about the rules and the procedures. Most of the people think that these American visas are being given to all the selected winners free of charge without any questions under this visa lottery program every year.
Actually the DV lottery program is not a simple draw but it is covered with strict rules and regulations.
If you don't read and respect them, you will lose the American entry permit along with your visa processing fees. Take note that there are only 50,000 entry permits available for any of the fiscal year program and normally 80,000 - 90,000 participants are being selected as winners.
Under this draw only submitting the entry form is free but if you are selected as a winner then you will have to pay for the visa processing fees not only for you but for all your dependant family members even if they are not intended to travel and settle in the USA with you.
Also there are some other expenses too must be met by the winner.
For to issue 50,000 American visas nearly 100,000 people will be selected as winners and will be asked to proceed with the winning under the normal immigration process to get one entry permit. So there is no guarantee that all the winners will be issued with the required entry permits or not. And the program is covered by closing date and time. Here are the main things that you will have to provide to the consular officer. By meeting all the eligibility and satisfying the interviewing visa officer is the only way to be issued with the USA entry permits.
Otherwise you will fail at the interview and the application will be rejected.
So these are some of the important things that can make a winner to be rejected at the time of the interview. It is important for you to read the current DV instructions carefully, before to start with the visa processing. Also you must read about the newly introduced E.O of the Newly elected American President's office.
Paid visa processing fee is also lost as it is a non refundable payment.
You can't re-apply or can't complaint against their final decision anywhere.