Yeah, I've done it too. Once it was at a place pretty far from my house. Fortunately, I realized it as I was walking to the bus stop. I had to backtrack about 3 blocks, but at least I remembered it before I got on the bus. Another time I got home and then noticed that I had forgotten a photo. I took the picture of the brand's area in the department store, but I was supposed to take a photo of the entrance to the store as well and I didn't. I was doing several visits that day, so I had a lot on my mind. I went back and took the photo to finish the report.
Once that same company in the second story above asked me to go take 3 or 4 exterior store pictures because another shopper had forgotten to do it. Not bad, they paid me US$10 for each picture, and they were all in the same area.