You scratch my back and I’ll scratch yours
Definition 1 of 1
Pro Tip 1/3Mutual Benefit
This phrase implies a cooperation where both parties get something in return. 
We can promote each other's businesses – you scratch my back and I’ll scratch yours.
Pro Tip 2/3Informal Setting
Use the phrase in casual conversations rather than formal or official communication. 
We're friends, right? You scratch my back and I’ll scratch yours, and we'll both pass this class.
Pro Tip 3/3Not Always Literal
Understand that the phrase is usually metaphorical, not about physical back scratching. 
If you help me with my website, you scratch my back and I’ll scratch yours when you need tech support.