He makes promises and he does not keep them. He should be consistent in what he says and what he does. If he is charming and kind this should show up all the time and across the board. You should see him being charming and kind to all people and not just you or just the ladies.You also want to look at how available he is. You should be suspicious if he has a lot of calls he doesn't take or if he sneaks off to take a lot of phone calls. It should also be suspicious if the number of calls he gets increases dramatically.
I was actually in that situation a few days ago. He will make promises but doesn't keep them. He tells you he cares but when he looks at his phone alot he is was texting another girl. You don't see him with his friends some days ? He is hanging with a girl. Don't trust someone quickly.