Now I’m 25 years old and all of these are my weekend hobbies. All you have to do is have a guts and bring a camera.

It’s a skill attained through trial and error. It’s a lot to do with blending in with the crowd; playing your role in the scene (as in, you’re reading things, having an interest in items, etc) and follow the “flow” of things. If you follow people very discretely for a few minutes (more experienced creeps can do it in a few seconds), you can easily pick out the “flow” that your target is going at. Maybe they are very fidgety, and turn around a lot – in which case you must make your shots more subtle. Maybe they are completely oblivious whores and won’t even notice you if you had a flash on directly on their ass. Anyway, find the rhythm of the dog and match it. Really that simple.

Pro tip: it helps if you carry an item roughly the size of your phone (if that’s what you’re using), and hold it against your phone screen so that when they turn around and look at your dirty red hands, all they see is the product because you swiftly rotate the angle of it and hide your phone beneath it. Works a treat. Good luck.