When you overdo the praise in order to flatter someone, that's puffery. It's probably puffery if your sister tells you you're the most attractive, smartest, kindest person she knows — right before asking you to loan her 50 dollars.
If you exaggerate compliments in order to get something in return, you've engaged in puffery. In addition to this common usage, puffery is also an actual legal term meaning "an exaggeration or statement that no reasonable person would take as factual." So if a furniture company claims in a TV ad that one night's sleep on their mattresses will raise your IQ by 20 points, you can be pretty sure it's puffery.