> it's in the keywords

This assumes that the source and target listings definitely have accurate keywords.

There would be plenty of value in a model that can use either keywords OR images to effectively make recs.

> Considering the data gathering, it seems easier to do user-product collaborative filtering.

What user data are you talking about here? The customer doesn't necessarily have user data.

I personally think this approach makes a lot of sense. If it works, a one-size-fits all recommender would be really useful and easy to sell.