Mern Stack Backend API Development

I need an experienced developer skilled in MERN stack to implement a backend API that will support my React frontend. The API will be dealing with various types of data, and the primary function of the frontend that needs support includes user interactions, data visualizations and e-commerce functionalities.

Ideal Skills:
- Extensive experience with MERN stack
- Proficiency in building backend API
- Strong understanding of React

Requirements:
- Ability to work with MongoDB, MySQL, and PostgreSQL
- Experience in handling user information, product listings and transactional data
- Capable of supporting various frontend functionalities with backend solutions.

Please provide examples of previous similar projects in your proposal.