what is buyer classification problem?
Buyer classification is used to categorize users who purchase groups of items. Buyers are categorized in order to be targeted for advertising. When users buy similar items, they are more likely to buy similar items in the future. This is useful information when pricing items on a website.

A clear example, a website selling nutritional supplements may want to target different buyers by category. Men in their 20s are unlikely to purchase menopause supplements, and women in their 50s are also unlikely to buy creatine. So, by analyzing user purchase history and categorizing types of buyers, the site can send intelligent promotions - males in their 20s get ads for creatine while women in their 50s get ads for menopause supplements.

Also, if I want to run a sale to attract customers, I don't want to offer lower prices on items which are often purchased together. I'd rathe price one low to attract the buyer, and then hope they buy the complimentary item at full price. Categorizing buyers also helps with this problem.

You may want to read up on shopping cart analysis, which is not a new problem. Department stores have been analyzing shopping carts and classifying buyers long before online shopping was popularized. That's why you have to use membership cards to get the 'special' prices.

Fine tuning these details can increase revenue substantially.