The ad on Facebook appears to be a scam; because, the boots are offered at a very low price. The boot in the attached photo is listed for $15.00.
The boot on the official Muck Boot Company website is listed for $115.00 https://www.muckbootcompany.com/
The official Muck Boot Company website states:
Is the URL suspect? muckbootcompany.com is the ONLY ecommerce site run by The Original Muck Boot Company® store; we do not have any online outlet or discount shops set up under different or similar URLs. We do sell to other legitimate third parties and you should feel safe shopping from any of those sites we link to from either our country selector or dealer locator page.
If the price discount looks too good to be true, it is.
If you should find a fraudulent site or if you have experienced fraud, you can report it here: https://www.bbb.org/scamtracker/us/