On a web shopping cart written in PHP, should I check IP address everytime?
Are too many people on rotating IP for this to be a good security measure (among others of course) or is this a standard practice?

Also can anybody enlighten me on some concepts I should pay particular attention to in securing a shopping cart? 

So far I have form validation, rotating session keys, no sensitive information is stored as a cookie or by javascript, SSL encryption, and all SQL is escaped.
On a web shopping cart written in PHP, should I check IP address everytime?
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Are too many people on rotating IP for this to be a good security measure (among others of course) or is this a standard practice?

Also can anybody enlighten me on some concepts I should pay particular attention to in securing a shopping cart? 

So far I have form validation, rotating session keys, no sensitive information is stored as a cookie or by javascript, SSL encryption, and all SQL is escaped.