Registration with stolen credit card is not that common among event registration transaction as there is no product to be send to receiver and it is not really possible that someone who paid registration fee with stolen card would appear on the event, but you might fall into trap when someone who paid with stolen card asks for refund by cheque. If you mail check to provided address, scammer can get it and realize it quickly. To avoid this danger, try not to do any exceptions while processing refunds. As a general rule, you should always refund a transaction by the method it was paid.
If your event is open for participants from foreign countries, you may have guests registering to your event only to get access to the country. If it is true, you will be probably contacted with request to send requesting a letter of invitation which will be required as part of their visitor's visa application. To avoid that kind of situation you should always question registrations from countries that you don't expect registrants from. Be suspicious for applicants, who are not really your targeted audience.
Another way to avoid scammers is to double check their personal information. As soon as somebody contacts you regarding registration made online ask some questions to verify their identity before offering them any information. If you ask questions properly the scammers shouldn't affect your event. There are platforms like http://www.businessvibes.com helping event organizers to stay in touch with visitors. Thanks to that risk of having scam visitors can be significantly reduced.
Marketing Executive - Europe
BusinessVibes Network Intrernational Inc.
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