Can you really earn $500 a day with Monster Mode?

Yes, but you need to put some effort in. Simply joining and not doing anything else will not make you money. Think of this as a business. You need to put some effort into it and promote it and at the start, results might be slow but as long as you put some effort in and bring a few people in then your income can really pick up. If you had 250 people on tier 5 that is 250 people sending you $20 if they buy.