"LIMITED TO 1 PER PERSON It's easy, buy one of these vouchers for only $10 and we will email you a unique voucher code for $20 that you can add to your Onceit account. PLEASE NOTE WE WILL EMAIL YOU WITHIN 48 HOURS WITH A UNIQUE CODE TO APPLY TO YOUR ACCOUNT."
Good for purchasing shoes, alcohol, clothing in general. You can stock them up and use them in one go (credit vouchers to apply to your account before use). Make sure you don't lose the emails (although you can ask customer service to resend the voucher codes) and do not use the vouchers for different accounts as the codes are acount specific.