It's up to you to make sure that you meet with this person enough times that you feel confidant that she will use YOUR likes, needs, wants, etc. into her design. Make sure that she is well experienced in landscape renovation, which is quite different than a complete re-do. She should also have ideas about how to provide you a new landscaping in stages, so that you can have a vision of what your property can look like in 2-5-10 years.

I've never done a design that I wasn't absolutely certain that the homeowner would like. It shouldn't be 'her' design, but a cooperation between the both of you.

Here's how it should work: you and the designer walk the property and discuss what you have, what works, what doesn't and where you're trying to go with all this. She then has the opportunity to show you her portfolio and possibly point out some things she thinks might resonate with you. IF you feel comfortable with her, like her style, and feel like you click, you can move forward to the next step, where money (and a contract) changes hands. Not comfortable? Feeling a disconnect? Keep looking, this is not the designer you are looking for.

I offer two things that provide my clients with peace of mind. First, I offer (for an additional fee to cover my time) to come out and meet to present initial concepts. This way, the client can weigh in on the direction the design is taking before I detail it out. I also usually include up to X hours of revision time in the contract, after which I state what I charge per hour for revision time.

So to answer the question of whether or not you need to pay the designer who has put in hours of work on your project? Yes! Why wouldn't you?

Some landscape designers/design build contractors might offer an initial consultation at no cost to meet and walk your site. Others that are more established and/or not as hungry for new work will charge for a consultation. Marcinde has addressed some good points that you'll want to consider regardless of who you meet with and how they charge.