We have all seen these kinds of sites that promise $8,000+ per month or worse yet per week within 30 days of starting their free program. 
Don't just walk away from these types of sites, run away.

Read Their Disclaimers:

Few people ever read the disclaimers on sites or the terms of sites, but you will be surprised what you find.  There is a company Rent-a-list.com and on their home page they tell you that you can find your customer fast, but if you read their disclaimer, I just wonder why anyone would buy from them.

An excerpt of their disclaimer is below.  I put the part in bold that kept me from trying their service and will keep me from every trying their service.

Clients using our advertising services more often than not do not report increase in leads, sales or profits, and many report losses. Successful results from our satisfied customers should be considered the exception rather than the rule. Clients utilizing our services can generally expect not to see any increase in sales, leads or profits. It is entirely possible you will lose money as a result of using our services.

Check Alexa and Whois information on sites

If you go to a site and it says they have been in business for X number of years, go check the Whois database and see when they registered the domain.

I was at one site and asked the owner how long he had been in business and when he told me 3 years, I checked the Whois and the domain was less than a year old. 

When I confronted him with this information, the conversation ended which was fine with me as he was a liar anyway.

Do Your Research

The bottom line is you need to do some research before you buy something online.  Avoid the instant money sites and the sites that promise thousands in 30 days and by all means avoid the site saying you can make $88,000 per month.

You need to walk before you run and you need to be able to build your business the way all successful businesses are built and that is one client at a time.