what are debt settlement basic rules?

are you looking for any company? bbb doesn't like settlement industry - why is that? please give more details

You're probably talking about the recent stripping of accreditation? I don't think that they object to the whole industry - just to some companies that have been getting tons of complaints (for underhanded practices), and bad entities do exist in all types of business. So the consumer has to do his homework before signing up to anything.

From the BBB:

BBB warns families that are drowning in debt to look for the following red flags when considering getting help from a debt settlement or negotiation firm:

• High upfront fees – Beware of companies that require large upfront fees before any debts are settled. Often, these upfront fees may be better used to reduce a consumer’s overall debt.
  
• Promises that are too good to be true– Some companies might promise that they can reduce debt by more than half even before looking into the customer’s financial situation.
  
• Claims that it’s a fast, easy and painless process. - Reducing debt through debt settlement takes time—often years—and can have a significant negative impact on the customer’s credit score. It can also expose consumers to lawsuits and garnishments.