Be sure that you include in your message some questions about it

such as “What is it about the MonaVie juice that justifies the price tag?” or “Why is a juice that is touted so highly by its company’s reps would be available for so much less on eBay?”

Don’t tell. Ask. YOU will never get them out, but you might be able to convince them to get themselves out. Be gentle, and make them think about the conclusions for themselves.