I hardly ever reveal. I do all of my outside observations before I go into the store. I make a note of the infractions. When I leave the store, I already know what photos I need and take them quickly and then leave. (I do the reports at home on the website.) For the other side of the ID, I usually drive to a safe spot and take that photo last.
That's just me, though. There is nothing wrong with being seen. If you don't want to be sneaky, just walk around the lot and do your thing. They probably won't even see you, and if they do, they probably won't say anything. Even then, you just tell them you are there for Citgo, and that usually ends the conversation. Don't even bother with the LOA unless they ask.
I try to be sneaky because I developed my system when I was automatically assigned a large group of locations I did every quarter, and I knew I would be back again and didn't want my cover blown. Now that these are assigned more randomly, that's less of a consideration.