You have two customers.

1 > experts

They have a problem: where can they find good clients who can afford their expertise? People who ask good questions?

2 > users

They have a different problem: where can they find competent, experienced experts who are available to answer their questions?

The users may want a discount on price. The experts would not like this. This is a branding & positioning question for you to answer.

You're going to have to get some early adopter experts to believe in and participate on your platform to demonstrate its validity.

Then the users will come.

Then word of mouth will take over to spread awareness that your platform exists.

Remember, this is a SOLUTION for people. Approach it that way. What's in it for them--not you.