Ditto question

I got five already, from rattatas and pidgeys. My theory is that, as he disguises as those but is still better, you could realize that circle color is not as its suppose to be and the mon is getting difficult to catch. Ex, a 200cp pidgey with the circle almost red? Isn't that weird? If i throw a red to it and escape, i quickly change to blue and razz and try better...
In this days so many of this "easy" mons had escaped and fled, i keep thinking they were Dittos...
Another thing is, if you see many of the same mons together... three pidgeys together, how come? ;)

As I understand it, the lower catch rate is the only indication before you actually catch it. And I read somewhere that the color of the circle matches the pokemon that it is disguised as, so you can't use that to help identify it.

Go to an area with a lot of pokemon spawns and other people playing. It will be a Ditto for everyone, and will be disguised as the same thing. If one person finds one, everyone else should be able to get it also.

You'll get one eventually - just keep catching the Pidgeys and Rattattas. With the double stardust there's no better time to focus on the common.

I caught 5 over three days but none today. All as either Rats or Pigeons. The low cp Dittos weren't obvious but the 570's that hid in Rats were obvious from how difficult they were to catch - they just kept bouncing out of the ball.

If I caught a Dratini and it hid a Ditto I think my phone would end up in the water (to be honest Ditto are so useless I'd rather have a Magicarp).

No giveaway that I could see- mine was just a normal 168 pidgey with a green circle, caught with one regular ball. Found one after 4 hrs of catching all the pidgeys, rattatas and zubats that I came across. Apparently they also come disguised as magicarps.

You need more luck. You better pray harder not try harder. I got 4 already and I pray everyday.

You should probably try looking around for a common pokemon that doesn't belong in that particular biome. For example, I just found a Magikarp in a residential area, far away from any water source. Turned out to be a Ditto.

Then again, right after that I found a group of Ratatas scattered around a 10 meters wide small area and one of them was a Ditto, so what do I know?