It's not the reliability of the SQL technology which is the concern. Like Lotus Foundations Server, MySQL has a ten year development history since the first Windows version of MySQL was released on January 8, 1998. MySQL is a core component in the open source LAMP development environment.
The problem is that getting your head around statements like...
FROM mowers WHERE price > 400.00
ORDER BY brand;
... is a big step when all you've been used to doing is a two column Data Sort on your spreadsheet and then scrolling down to find the right price point. I can sympathise with the fear factor but ignoring that challenge will keep your business permanently down at the S end of the SMB market.
Unfortunately I can't teach you SQL in a half-page blog entry. You can read more about MySQL at the MySQL home page or if you want some free on-line training for MySQL then check out a combined PHP-MySQL tutorial or Tizag, or for a more advanced developers try MySQL Tutorial or Tutorials Point.
BTW MySQL is also a good a strategic investment for larger organizations that are trying to wean themselves off the habit of paying annual licence fees to Microsoft for SQL Server. Reminds me of that anti-drug campaign from years ago...
Just say No!
Just say No!