Not sure it's worth the added time and effort to make sure you are hiring the right programmer? Here's an example of why the time is worth it:
A client hires a new consultant. They have a database with about 4 million records, and then need help exporting some of the data to Excel. The previous consultant used a query that grabbed ALL of the columns, so the file was quite large. The new consultant asked if they really needed all that data. Guess what? They only needed 5 columns, so the new file was about 20% of the size!
Then the customer complained that the previous consultant told them that they had to manually remove all the places where it said "NULL". They spent 4 DAYS doing this. The new consultant spends a few minutes tweaking the query and boom: the data no longer has any values that say "NULL".
This is true story. The new consultant saved the client a ton of time for downloading and data tweaking. Was the previous consultant incompetent or lazy? We’ll never know, but one thing is for sure: the new consultant has proven their worth to the client!