Building on what @Santos_miles mentioned.
If you created a job within the Experts Marketplace, then it would be normal for a Shopify Expert to be contacting you as they believe they can assist you with completing the job you've posted. That said, if you haven't created a job within the Experts Marketplace and this Expert is cold contacting you, in that, they have no reason to contact you, then I would advise against hiring them.
We always recommend hiring from the Shopify Expert marketplace. Platforms such as Fiverr have do not verify "Expert" status, meaning that anyone there can claim they are a "Shopify Expert" even though they haven't earned the status with Shopify.
In the event that you were contacted by an "Expert" through the Community, then please report the message by clicking "Report" when you have the message open. Doing so will allow the moderation team to review the interaction further.