There is always a way to break the user password unless it's designed for strong encryption and security. I don't think any repair shop will know how to do it for a Mac since Macs are serviced by Apple usually. Repair shops are also pretty stupid usually.
With Windows XP, Vista, 7, you can break the user password with Linux. MacOS is based on Unix so I think there will be a similar way but I am not familiar with it as I am with Windows. Someone else can chime in or I (or you) can google it up.
If all else fails, just format the computers and reinstall OSX or leave the users and create a new user. You only need to break the password if you need to save personal files and documents associated with and protected by the account. I would just blank the computers and reinstall the operating system from scratch.
edit:
Just google yourself, this is the very first result in google.
http://lifehacker.com/278898/reset-y...-os-x-password
Code:
Hold Apple+S when booting to enter single user mode
#sh /etc/rc
#passwd yourusername
#reboot