Begin by accessing the Zendesk Sell API to gather the data you need to transfer. Ensure you have an active API key or OAuth token from Zendesk Sell. Refer to the Zendesk Sell API documentation to understand the endpoints and data structures available. For instance, if you need to retrieve contacts, you will use the `/contacts` endpoint.

Use a programming language of your choice, such as Python or Node.js, to send HTTP GET requests to the Zendesk Sell API endpoints. Parse the JSON response to extract the data fields you require. For example, use Python's `requests` library to fetch data and convert it into a manageable format like a list or a dictionary.

Once you have the data, transform it into a format suitable for Redis. Redis primarily stores data as strings, hashes, lists, sets, or sorted sets. Decide on the data structure that best suits your use case. For instance, if you're transferring contact details, you might use a Redis hash where each contact's ID is a key, and the contact details are fields within that hash.

Ensure that you have a Redis server set up and running. You can install Redis locally, use Docker to run a Redis container, or access a Redis server in the cloud. Confirm that you have the necessary permissions to write data to our Redis instance.

Use a Redis client library in your programming language to connect to the Redis server. For Python, you might use `redis-py`, and for Node.js, you could use `ioredis` or `node_redis`. Establish a connection by providing the host, port, and any authentication credentials required.

Iterate over your transformed data and use the appropriate Redis commands to store the data. For instance, if using Redis hashes, you would use the `HSET` command to add each piece of data to Redis. Ensure data consistency and handle exceptions, such as connection timeouts or data format errors, during this process.

After transferring the data, verify that the data in Redis matches the original data from Zendesk Sell. You can achieve this by retrieving a subset of the data from Redis and comparing it to the original dataset. Implement logging to track the success or failure of data transfers for future reference and troubleshooting.

By following these steps, you can manually move data from Zendesk Sell to Redis without relying on third-party connectors. This approach gives you full control over the data transformation and transfer process.