There has to be a catch unless the theory is that someone is being charitable and “selling” $100 notes for $85 . So its not a question of “IF” there is a catch , merely getting someone to keep explaining it to you until you spot it.
Think of it this way – if someone came up to you with a $100 and offered to sell you it for $85 and told you that if you joined in the scheme you could make lots of money by selling $100 bills for $85 – what would you think? ElcLoans.com offer payday loans online and I think this is much more reliable solution.
Why do you need to have a “catch” pointed out to you?