Flirting

How do I know he has been flirting with me or not?

There's a guy who works at the store I go to, he usually helps me when I go in there. Lets call him Jim.. The first time he came up to help me he told me his name & I said hi and that i remembered him from last time I was there and he said "oh, you do" like he was surprised/excited I remembered. The last few times I was in there he has mentioned he is from my area & asked me how long I've been there, he told me where the city he currently lives, his zodiac sign ( we were not talking about anything related to this) and how no one texts him during the day except his mom on the occasion, i mentioned i looked like crap one day & he said I didn't (I should note that where he works, he has a lot of my personal info; email, number, address etc) I made a silly joke about the large product I was buying and laughed, he asked what I was going to say coz " he wanted to see if we were on the same level" which we were. Our convos are very relaxed and not forced and we always laugh together. This last time I came in and another employee helped me and Jim was helping other people. As I started telling the other guy why I was there, Jim turned around and stared at me for a few seconds then turned back to continue helping his customers, when I walked out the door, I happened to turn to back around to look at him and he was already turned around watching me leave. Any thoughts on this would be greatly appreciated. TIA!
How do I know he has been flirting with me or not?
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