What is the best way to prevent customers from rating a product more than once?

Question

How do I prevent a customer from rating a product more than once? Is it best to use cookies that store the IP address or is it best to store user ratings in the database? I am using MySQL and ColdFusion.

Cheers!

Answer 1

If you have user accounts, associate your ratings with the accounts. Job done as long as one user only has one account.

If you use cookies then you will likely run into problems with users who have them disabled, who use multiple browsers or who deliberately delete them, if you store the IP address you will potentially ( although it is quite unusual ) run into problems with different users from the same IP address- the same family or organisation will probably have relatively few external IP addresses, while ISPs such as AOL will routinely have requests for a single page come from multiple IPs.

On the whole my feeling is that if a user cares enough to rate a product they probably care enough to sign up for a user account. You can still keep an eye on IP data and other browser information in case anything dodgy is going on, but that is the most effective way to ensure that your users are at least distinct enough to have different email addresses. It won't catch anyone wanting to seriously manipulate your ratings, but actually if you do run into someone like that you will have a hard time stopping them whatever you do and until you have indicative useage patterns you'll be hard pressed to know what to look for. In this instance making sure that whatever you do, you keep careful logs is important...

Answer 2

If you can store the ratings in the database, go for it. Cookies can be deleted and IP addresses can't be used to reliably identify a particular person.

Answer 3

Well, all of your rating proceedures once rated will communicate with a database right? Since you are using mySQL each rating will presumably be saved in your database.

When you have rated a product, just give the user a unique ID, based on his IP, or if applicable a username. Then check to see if this user has already rated once before.

Its quite simple.

 IF userVoted != true 
         saveVote ( "ipAddress", "User Voted Yes")
    else
         display ( "You have already voted" )