“You scratch my back and I’ll scratch yours” is a famous business proposition, similar to the Latin quid pro quo. “Scratch my Back, and I’ll claw your Elbow” was cited in the London play, The Comical History of Don Quixote (1694). “Scratch my back, and I will tickle your elbow” was cited in an American newspaper in 1807.
 
“The vulgar maxim you ‘scratch my back and I will scratch yours’ was happily illustrated” was cited in an American newspaper in 1821.
     
 
Wikipedia: Quid pro quo
Quid pro quo (“something for something” in Latin) means an exchange of goods or services, where one transfer is contingent upon the other. English speakers often use the term to mean “a favour for a favour”; phrases with similar meaning include: “give and take”, “tit for tat”, “you scratch my back, and I’ll scratch yours”, and “Skid row bro.”
 
Wiktionary: you scratch my back and I’ll scratch yours
English
Proverb
you scratch my back and I’ll scratch yours
1. If you do me a favor then I will do you a favor; quid pro quo.
   
Google Books
The Comical History of Don Quixote
By Thomas D’Urfey
London: Printed for Samuel Briscoe
1694
Pg. 16:
...  besides, you know the old saying, Scratch my Back, and I’ll claw your Elbow; ...
 
28 September 1807, Green Mountain Palladium (Chester, VT), pg. 3, col. 3:
“Scratch my back, and I will tickle your elbow.”
       
8 February 1821, The Pilot (Cazenovia, NY), pg. 2, col. 2:
The vulgar maxim you “scratch my back and I will scratch yours” was happily illustrated.
 
Google Books
August 1833, The Dublin University Magazine, “Travels of an Irish Gentleman,” pg. 149, col. 2:
Here he is introduced to a certain professor of theology or rather of neology, whom he names Scatchenbach, in plain English Scratching back, a very appropriate appellation, implying the agreement of mutual and responsive assistance between Popery and infidelity, whose co-operation in attacking the bible is well illustrated by the vulgar adage — “scratch my back and I’ll scratch your’s.”
 
4 April 1839, Florida Herald, and Southern Demcorat (St. Augustine, FL), “The Bank holds abundant Security,” pg. 2, col. 4:
What a deal of “you scratch my back and I’ll scratch yours” there must have been among the originators of this scheme!
 
Google Books
October 1853, Graham’s Magazine, pg. 394: 
Bussassa came round at once, and on the principle of “you scratch my back and I’ll scratch yours,” declared that young English gentlemen had no fear, and required prudent Shicarees to keep them out of danger.
 
OCLC WorldCat record
You scratch my back and I’ll scratch yours. [Song.].
Author: Edwin V Page
Publisher: London, [1881]
Edition/Format:   Musical score
 
Google Books
A Book of Quotations, Proverbs and Household Words
By W. Gurney Benham
Philadelphia, PA: J. B. Lippincott Company
1907
Pg. 846:
Scratch my back, and I will scratch yours.
 
Google Books
15 June 1913, The Mixer & Server, pg. 58, col. 1:
SCRATCH MY BACK AND I’LL SCRATCH YOURS.
Rather an inelegant expression, yet one which brings right home to many of our members, or should, the perturbing thought that we seek support and co-operation of other trades and callings to advance our trade interests and promote the welfare of our organization, but somehow or other, we frequently overlook pushing and boosting for the men and women who accept our invitation ot help us.
 
Google Books
April 1917, The Rotarian, pg. 342, col. 2:
Other clubs may have had the “You scratch my back and I’ll scratch yours” idea but neither its founder nor his immediate successor in the presidential chair ever held to this plan for our club.
 
OCLC WorldCat record
You Scratch My Back and I’ll Scratch Yours: Continuities in Inuit Social Relationships
Author: John S Matthiasson
Edition/Format: Article Article : English
Publication: Arctic Anthropology, v12 n1 (19750101): 31-37
Database: JSTOR Arts & Sciences VI Collection
 
Urban Dictionary
You scratch my back, I’ll scratch yours.
You do me a favor, I’ll do you a favor.
This time, I’ll fix your car for free. You scratch my back, I’ll scratch back!
by Xiao July 16, 2002
 
Google Books
Safire’s Political Dictionary
By William Safire
New York, NY: Oxford University Press
2008
Pg. 399:
The classic description of the theory of logrolling is attributed to Simon Cameron, Pennsylvania politician who served as Lincoln’s first Secretary of War: “You scratch my back and I’ll scratch yours.”
   
OCLC WorldCat record
You scratch my back and I’ll scratch yours : mentor-perceived costs and benefits and the functions they provide their protégés
Author: Julia M Fullick
Publisher: Orlando, Fla. : University of Central Florida, 2008.
Dissertation: Thesis (M.S.)—University of Central Florida, 2008.
Edition/Format:   Thesis/dissertation : Document : Thesis/dissertation : State or province government publication : eBook   Computer File : English
Database: WorldCat
Summary:
Mentoring relationships can have both costs and benefits for mentors and their protégés. The present research examined the degree to which mentors’ perceived costs and benefits affect the functional and dysfunctional mentoring they provide to their protégés. Additionally, I investigated whether mentor-perceived costs and benefits were associated with the mentors’ own goal orientation and the goal orientation of their protégés. Data were collected from 86 protégés and their current supervisory mentors. Consistent with expectations, when mentors reported greater costs of embarrassment associated with their relationship, the protégé reported receiving greater dysfunctional mentoring. Protégés who reported receiving greater functional mentoring tended to have mentors who perceived greater benefits of mentoring them. Both protégé and mentor goal orientations demonstrated significant correlations with mentor-perceived costs and benefits of their relationships. Implications for training and reinforcing functional mentoring will be discussed.
 
OCLC WorldCat record
“You Scratch My Back, I’ll Scratch Yours”: Reciprocal Intraprofessional Collaboration for OB Simulation
Author: Kathryn R Alden Affiliation: UNC Chapel Hill School of Nursing, Chapel Hill, NC; Lisbeth Coulombe Affiliation: UNC Hospitals, UNC Health Care, Chapel Hill, NC; Jennifer Taylor Alderman Affiliation: UNC Chapel Hill School of Nursing, Chapel Hill, NC
Edition/Format: Article Article : English
Publication: Journal of Obstetric, Gynecologic, & Neonatal Nursing, v42 ns1 (June 2013): S9
Database: Wiley Online Library