To clarify as much of the concept as possible before discussing on call
While I appreciate prior documents or assets being shared, it's best to review the ToS and verify if there is an NDA included in it. With marketplaces, such as Upwork, there are NDAs that are implicit when contracting. Not sure if it's on here.
That's certainly up to the ToS and expert. They may choose to take the PDF/SlideShow beforehand to prep for the call. If you are providing the clarity, that may be fine. Indeed, I often ask for a certain amount of conceptual clarity so I don't spend too much of the client's time and money during the call.
However, to ask experts to do any work on it, or for oneself to ask an expert for clarity before the call is, I'd argue taking advantage of the expert's time. It's entirely possible for unscrupulous clients to get the clarification they need before a call and then never take the call, thereby getting the service for free. It risks leaving the experts out of pocket, potentially twice, if they've given up other work to take that call. It's why Clarity as a platform, exists.
Hence, as both a matter of safety and respect, most customers should not ask to get any clarification without paying for it. Most experienced experts who have been in this game for a while will be aware of such risks and sensibly won't offer clarity without payment for it.
I hope that helps and best of luck for your session!
You could certainly ask the expert about that. In my view, it's in the interests of both you and the expert for that to happen.
The expert isn't working for free. Perhaps the expert will only look at the material once you have confirmed the call time. That gives you (as a client) more of a commitment to this expert. But you don't get any feedback until you get a paid call.
As someone who offers advice over Clarity re positioning and pricing, it is certainly in my interest to give the very best advice I can. An important component of that is to do what research I can do ahead of time, so being able to have at least a quick look at a website, a slide deck or a short PDF, before the call makes for a better quality call.
Better calls = better reviews, which is attractive for other potential clients.
For example, supposing a creative design agency contacts me and says: "we need help with positioning ourselves in the market. Our clients are comparing us with Upwork." If I have some background on this particular design agency, by assessing [for example] that they impress visitors with their amazing designs, but that rarely leads to conversions, then the call will be more efficient. Shorter calls are likely to build trust for longer calls and perhaps other project work.
I respect the decision of experts who say: "no, we'll look at this once the meter is running." That is also a good sign, that they are respecting their own time, which increases their perceived value. But reviewing on the spot may require some quick thinking, and being prepared ahead of time makes for a better result for the client, in my view.