将帐户限制为每个用户1个 - PHP

The website that I am currently designing has run into a bit of a snag - basically my client has mad it clear that he needs a one person = one account feature, now I'm not the best at analytic's (despite my programming background) so I could really use some suggestions.

We are programming in PHP, and I'm 100% aware that there isn't a solution that would 100% prevent the problem, but I need as close to the 100% as I can get and so far I have tried...

  1. Placing cookies to the users browser. Workaround - Switch browser.
  2. Tracking IP. Workaround - change IP, reset router etc. (Also, more than one user per IP is permitted).
  3. Using analytic's to try and track actions such as Account A being logged out, then a minute later account B logging in from the same IP. (This seemed to be the most effective, but it took a few people to keep it going so I'd like to automate it as much as possible or if possible eliminate the need for manual monitoring.

The problem is that the users of my clients site will be paid depending on different actions and my client has already decided on a $10 minimum withdraw amount, and payments will be handled via PayPal.

So basically multiple account usage could cost my client a lot of money if the site goes live without these features.

I would also like to keep this back-end (possible cron-tab). Just to be clear.

Any help/input/suggestions at all will be massively appreciated.

Tah

PS- I have already checked out this question (Account verification: Only 1 account per person) which is where I got the idea for point 3 from.

The only way to really prevent a person from signing up for multiple accounts would be to ask them for personal information specific to them. I ran into this issue and ended up having to track social security numbers to prevent multiple accounts. Granted, the project I was working on was for a school and the school already had this information. Also, for a new user signing up, it wasn't unusual to them to give this information.

Reading some of the comments, I can say that even if PayPal had a way to track duplicate accounts, it is highly unlikely that you would be granted access to this information, even just to say "yes this is a duplicate" or "no it is not a duplicate".

I really think SSN would be your best bet.

AFAIK iovation uses a set of tracking methods, including Flash cookies and browser fingerprinting to track the users and the devices used. Although budget-wise it might not be your best option, you may consider the techniques themselves.

I'd suggest the business to create incentives for using a single account, which might pay off better than (costly?) fancy tracking software.