Flattery is one of those things that can very easily go from sweet and appreciative to insincere and phony in 2.8 seconds. Much like with everything else in this world, it all comes down to how you say it, not necessarily what you say. The phrase “Wow, that looks really nice on you” can sound both positive and smarmy, depending on the tone of voice and body language used. It’s always nice to be complimented and praised for something, whether it’s how you look or a project you’ve completed at work or some landscaping you did at your house, but where a lot of people fail is not making it sound like you’re trying too hard. Telling someone they look lovely is great. Telling someone that no woman/man has ever looked better than they look right then in that moment and everyone else pales in comparison just sounds too OTT to be anything other than fluff. They may not mean it to be OTT, but that’s how it comes across. There’s nothing wrong with being more measured in your language, even when complimenting someone. There’s a fine line between sincere and insincere.