Best Way of Finding out How a Customer Purchased a product

Question

What is the best way to find out if a customer has purchased a product instore, as a result of visiting the website? Would a membership card be a good idea, or something like an email newsletter with offers for that specific store? Keeping in mind, the product may only be bought less than a handful of times in a few years.

Answer 1

If you give a product a unique code, in addition to it's web id. The unique code could only be redeemed instore in exchange for a free gift or instore only discount. That way the volume of sales can only be attributed to the unique code!!

Volterony