By definition, there isn't a difference between a handler and a pimp. There's more negative connotations with the word pimp and a sort of stereotypical mental image when you think of it, but by definition both handler and pimp are someone who deals with the booking on behalf of the SP, in return for taking a percentage of the income. Technically speaking, every single sw agency is acts as the handler for the girls in their employ.
Now, whether or not being a handler is inherently exploitive is a whole different issue. Handlers (and agencies) do provide a service, such as owning the incall space, taking care of advertising and booking schedules, providing security etc. Again, it's not the stereotyped image of some gangster in a fur coat abusing women. That said, some handlers ARE exploitive, you're just going to have to do your research.
Your best bet, if you want to complete avoid any ambiguity, is to only book with established ladies that have their own websites or social media presence.
