Welcome to the real world bud. More often than not you will run into such things regardless of setting. Inevitably you will become keenly aware of signs people give out and it will be as if a sixth sense to weed them out.
They have always existed everywhere but they are much more spotlighted now due to the world becoming so much smaller due to the internet. Just take them in stride, learn their tell signs/mannerisms, and never forget them because no matter what walk of life or path you take, you will always run into them.