Most of the time the people who begin with this as the opener of the conversation, they are unattractive.
Sorry if that seems too harsh and judgmental but it's the dang truth. ALSO don't begin with:
"I know you hear this all the time, but you are very pretty."
No dude, to be honest I don't hear it all the time because I don't hang around player jerk faces like you 24/7.
Genuinely, a guy who is attracted to you will keep it to himself until the right time comes and not rub it in your face all the time. Most likely, a guy who is constantly telling you over and over that you're beautiful/sexy/pretty etc. they are covering something else.
I went through an extremely abusive relationship for a couple years, and he showered me with words of kindness and telling me I was sexy and beautiful ALLLLL the time. It wasn't til the relationship ended that I realized he wanted me to believe he loved me and was attracted to me so I wouldn't see what he was really doing to me. My guard is up when it comes to a guy constantly telling me I'm pretty/beautiful/sexy. ESPECIALLY if that's their opener!
Hey how are ya?
What's your name?
I'd like to know more about you!
Obviously you think I'm attractive or you wouldn't have contacted me- that's what online dating is based on- your pictures.