This is a "you scratch my back and I'll scratch yours" approach to negotiation. What is it?

It generally means a favour for a favour, but in no way can it be used in a formal or professional situation. This more applies to an casual agreement on a personal or individual level. As Goutam pointed out, reciprocity would be a more apt term in any representative negotiations.

It is reciprocity. In negotiation , reciprocity is a mutual or cooperative exchange of favors and privileges. It is exemplified by the American Expression " You scratch my back and I'll scratch yours ".

exchange benefits or favors and privileges

Proverb:If you do me a favour, I'll return it.

Simplest Example:Can you Endorse my skills in return I'll endorse yours :)