You should be wary if

• the cover features "from one of producers of"
• the film gets four stars from Caravanning Monthly.
• this is the only review to feature on the poster or TV advertisement.  
• you have to spend over a certain amount to qualify for the additional advertised saving.
  
• it comes with "free appliances".
  
• the company, for no good reason, uses an umlaut in their name.
  
• they offer you a points / loyalty card.
  
• it says "for illustration purposes only."
  
• it says "serving suggestion."
  
• the product features a nutritional serving / portion size on the packaging divided by any number other than 1.
  
• it's a once in a lifetime offer.
  
• they promise no salesperson will call.
  
• it's risk free.
  
• it's cached in equivocation, such as "up to 100%".
  
• they claim it's 100% natural.
  
• the APR is the sharp side of 2500%
  
• it's void where prohibited.
  
• it produces an oily residue.
  
• it's a miracle. 
  
• it's revolutionary.
• it's benefit has a three letter acronym.
• their ad features a golfer. In a Pringle jumper. And a baseball cap.
• their slogan talks of "synergies" (or any derivative)