you scratch my back
"If you scratch my back, I'll scratch yours" is used to say that if you help me I will help you, as is clear from this headline and article from the Daily Mail about Kelly Brook:
You scratch my back, I'll scratch yours: Kelly Brook gets help from the ever-present paparazzi with her huge suitcase
She is a prolific model with a huge fan base, so it's no surprise the paparazzi follow Kelly Brook's every move.
And after giving them many shots of her looking groomed and glamorous over the years, the star turned the tables and asked them to help her - with her huge suitcase.
It seems that even paparazzi are not all bad.....but if you are not rich and famous you may try to win some money by buying a scratch card and revealing the symbols or numbers to see if you have won a fortune. If youare not so lucky that you'll have to continue to scratch a living - earning just enough to live on, with difficulty!