Begin by logging into your Smartsheet account and navigating to the sheet you wish to export. Use the "File" menu to export your data in a CSV format, as this is a universally accepted format that can be easily manipulated for import into PostgreSQL.

Ensure that you have PostgreSQL installed and running on your machine or server. You should also have access to a PostgreSQL client or interface, such as pgAdmin or the psql command-line tool, to interact with your database.

Create a table in your PostgreSQL database that matches the structure of your Smartsheet data. This involves defining the appropriate columns and data types. Use SQL commands such as `CREATE TABLE` to structure your database table.

```sql
CREATE TABLE your_table_name (
column1_name DataType,
column2_name DataType,
...
);
```

Open the CSV file exported from Smartsheet using a text editor or spreadsheet software like Excel. Check for and clean any inconsistencies, such as missing data, incorrect data types, or special characters that might disrupt the import process.

Utilize the PostgreSQL `COPY` command to import the data from your CSV file into the created table. This command is efficient for bulk data import and requires specifying the path to your CSV file.

```sql
COPY your_table_name (column1_name, column2_name, ...)
FROM '/path/to/your/file.csv'
DELIMITER ','
CSV HEADER;
```

Ensure the file path is correct and accessible by the PostgreSQL server, and that the CSV headers match your table columns.

After importing the data, verify the integrity of the data in your PostgreSQL table. Run queries to check for discrepancies or errors that might have occurred during the import process. Use SQL commands like `SELECT` to sample the data and confirm its accuracy.

```sql
SELECT * FROM your_table_name LIMIT 10;
```

If you need to perform this data transfer regularly, consider writing a script (e.g., in Python or Bash) to automate the export from Smartsheet, cleaning, and import into PostgreSQL. This will save time and reduce manual errors. Use libraries like `psycopg2` in Python to interact with PostgreSQL programmatically.

By following these steps, you can effectively transfer data from Smartsheet to PostgreSQL without relying on third-party connectors or integrations.