There are identifiers that you can specify in the froogle feed (from the site owner) that tell Froogle the manufaturers ID for a product. If people use this code then it allows like-for-like comparisons. It sounds good in theory but e-commerce sites often adopt their own codes for products to fit into a single format. Imagine you supply products from a dozen or more suppliers, it's tempting to put a 2 letter or digit prefix to the codes and then go numeric from there.
If a site used this at the beginning it's going to be a real nightmare updating 20,000 items with manufaturer codes. I know of a few sites that have this problem as they do not have 100% automated processes and hence cannot easily extract the unique ID that would help them.
Apart from using the above codes Froogle is just guessing that products are the same, and even then people write descritions differently, mistakes are made on inputting item numbers etc. Good comparisons are not easy to make.
