I had the same problem, but after some thinking I think I have some guidelines to follow.
1) Don't come over as too professional, otherwise she will not see you as a potential b/f. Having said this, try to keep a degree of professionality about you, so she doesn't see you as a goof off.
2) It's not what you say (to a degree) but how you say it that counts. Make sure that everything you say is finished with a cheeky smile, so she knows you're a fun guy to be around. Also, ensure that you speak clearly, because it's quite embarrassing if she can't understand you!
3) Let her know when you're in the shop at the end, if she needs any help with any of the stuff, so she has an excuse to come back and see you, without having to admit to herself that she is just coming to see you!
I'll try and make this situational. Say she comes over to pay for hay for example:
You: 'Hay? Unusual for humans to live in barns nowadays y'know?' (Cheeky smile) That'll be $x please.'
Her: (Grins) Sure.
You: 'Do you want to know something interesting (touch yourself when you say interesting, NLP) about hay? (cheeky smile) Choking on hay is the number one killer in Moldova.'
Her: 'No way!/Really'
You: 'I swear, it's true! Look it up! Anyway here's your stuff. Now if you ever feel the urge to brush up on your hay knowledge, you know where to come.'
If you perform this right, then she should come back with positive connotations of you, and will be the one trying to talk to make conversation with you next time!
Hope this helps
Dougie