This happens to me almost daily no matter how I look that day. I started wearing a wedding ring long before I got married to have an easy out. Usually, guys are just being nice. Sometimes they're trying to gauge if you're interested. Depending on how you respond, they try to figure out if they have a chance.
Don't fall head over heels in love with the fantasy of what could be! Know for sure he's interested before you get all wrapped up in it.
If you're interested in getting to know him better (and he's age appropriate, seems nice, etc.), then go to the store more often, smile at him, and see if over time he gets comfortable enough to make a move. Let him be the one to step out on the ledge... but send the send the signal that he won't plummet to his death.