When a use adds an item they should have the option of adding alternatce versions if the "same" item.

For example - a user might be happy with ASDA own brand beans or ALDI brand beans - but letting the user add alternatives from other shops it helps to find the best price for the shopping.

This data can be learned-from to provide suggested alternatives for the user. There would also be the option of using this data to procide better search results and even helping other isers to find alternatives also.