Retailers can often get product data directly from the manufacturer. This is true 100% of the time when the retailer is drop-shipping. The problem isn't really obtaining this data but the canned data you get is pretty worthless. Thousands of online retailers were hit hard by the Panda update (some time ago) because they all used the exact same descriptions provided by the manufacturers. So a lot of time was spent on custom descriptions and "romance copy." If you can find a way to offer unique product descriptions or at the very least somewhat unique then you could save these companies money.
Another problem online retailers face is categorization. Not on their own sites but with mapping their items to the various taxonomies employed by Amazon, Buy.com, Shop.com, PriceGrabber, and so on forever and ever. Find a way to provide the mappings to each of these company's taxonomies and people will pay you. The alternative is doing it all by hand, using a script to cover most of the ground and doing the rest by hand, or by outsourcing it. If I had a service at my finger tips that could have done all that for me when I needed it, I'd have happily recommended it to the boss.
You should charge for these services, of course.