Jack Weasel's the sheriff around Coveland, the main country where the story takes place, and Hope is one of three top-ranked Bounty Huntresses, so often their paths cross one another. Typically, it results in a tussle when her sisters are present, but if he can get her seperated, he flirt a little and get her off guard. While it all looks good in the business sense..
..he just likes to flirt with her. :P