API Code Writer/Creator

Applicant should be experienced in writing Application Programming Interfaces, I need an API written to connect my WordPress membership site to Motorcycle Dealers sites to transfer motorcycle sales data from their sites which most will be written in custom PHP and HTML code to my WordPress coded site. The dealers will sign up and join my membership motorcycle sales site and will obtain and install my API to their site and the API will be written and programmed to transfer their motorcycles for sale info, including pictures, color, basic description, to my site for viewers to see, The API should work automatically over night on a regular basis to update and add new vehicles and delete sold vehicles from their site to mine.
Pay will be on a gig project basis and discussed upon interview.