First of all, don't scrape, and don't call what you're doing scraping. Scraping immediately connotes theft in the sense of taking something which is not meant

First of all, don't scrape, and don't call what you're doing scraping. Scraping immediately connotes theft in the sense of taking something which is not meant to be taken. Instead, index. Indexing, on the other hand, connotes supplementation in the sense of adding value to that which is already there. Have the thumbnails, excerpts of the descriptions, and whatever secret sauce you've not mentioned add value to the owners' data. Provide traffic or some other measurable benefit to them. Don't rely merely on Fair Use (or weak interpretations of the doctrine). Provide value to the data owners, and be ready to respect their wishes if they chose not to accept the value proposition you offer.