I have already done what you suggested and contacted the business to ask if the purchased the photo. Their response is that they did purchase it, but they provide no proof of doing so. Adobe has not responded to my request asking if that business has purchased this photo. It's frustratin g to not get help from Adobe as the seller of our photos.
Hi Kirk,
If you are going to sell stock photos, get accustomed to seeing them in use. I have tens of thousands of sales across 5 different sites of photos and videos. I see my photos in use on websites all the time (check out tineye.com to find where your photos are being used). I see my footage on TV all the time. If I tried to verify the buyer and the agency each time I saw my media being used, it would be a full-time job in itself. I know my media is not being made available without watermark, so if I see my media in use, I am confident it has been properly licensed.
The one exception to this is if you find your media available for resale, on merchandise. Different sites have different contracts for using media for resale. I encountered one of my photos being sold as a photography backdrop. In that instance, I did contact the agency, and they did verify that the buyer did not purchase the proper license for resale, and they went after them, and gave them the option of purchasing the Extended License, or cease to sell the product. The product was removed from their site.
Brad has a good point - do you have these photos available somewhere where they are not watermarked?
My advice is that when you see your photos in use, use it as momentum in knowing you are providing commercially viable images, and create more! 