"you seem really sweet" = "I think you're easy to manipulate / you seem vulnerable and I want to confirm it depending on how you respond to this compliment".

Never trust a guy who tells you this. Every single time I've been told I seem sweet the guy ends up trying to test the waters for how much he can disrespect me and get away with it :)

Edit : just wanted to add that "you're a good person / a kind girl" = "you let met step all over you boundaries without putting up a fight". My ex has told me this over and over and I only now realized that's what he meant.