First, log in to your Smartsheet account and open the sheet you want to export. Use the "File" menu to select "Export" and choose the CSV format. This will download your sheet as a CSV file, which can be easily manipulated and imported into Snowflake.

Review the exported CSV file to ensure data integrity. Check for any formatting issues, missing values, or inconsistencies. Make adjustments if necessary to ensure the data is clean and ready for import. Save the file in a known directory on your local system.

Log in to your Snowflake account and navigate to the worksheet area. Use the SQL editor to create a table that matches the structure of your CSV data. Define the table schema accurately to include column names and data types that correspond to the data in your CSV file.

Example SQL:
```sql
CREATE TABLE my_table (
column1 VARCHAR,
column2 NUMBER,
column3 DATE
);
```

Use the Snowflake UI or SnowSQL command-line tool to upload your CSV file to a Snowflake stage. If using SnowSQL, execute the following command to upload your file to a named stage:

```bash
PUT file://path/to/your/file.csv @my_stage;
```

Ensure you replace `path/to/your/file.csv` with the actual path to your CSV file and `my_stage` with the name of your stage.

Once the file is staged, use the `COPY INTO` command in the Snowflake SQL editor to load the data from the stage into your table. You may need to specify file format options to match your CSV file's characteristics.

Example SQL:
```sql
COPY INTO my_table
FROM @my_stage/file.csv
FILE_FORMAT = (TYPE = 'CSV', FIELD_OPTIONALLY_ENCLOSED_BY = '"');
```

After copying the data, run a simple `SELECT` query on your Snowflake table to ensure that the data has been imported correctly. Check for data integrity, correct data types, and that the number of records matches your expectations.

Example SQL:
```sql
SELECT FROM my_table LIMIT 10;
```

Once you have verified that the data is correctly loaded, remove the CSV file from the Snowflake stage to save storage space. You can also apply any necessary optimization techniques, such as creating indexes or clustering keys, to improve query performance on your newly imported data.

Example SQL:
```sql
REMOVE @my_stage/file.csv;
```

By following these steps, you can successfully move data from Smartsheet to Snowflake without relying on third-party tools.