In a few cases where the code signing allows, you can prevent this check.
- In finder, right click each app and show package contents.
- Locate a folder named _MASReceipt and delete it.
This removes the receipt that tells the App Store to manage the app. I would do a backup of all apps before you alter them in case you want them back without downloading the update you seek to avoid.
In many cases, this wrecks the app since it’s now been tampered with - How do I avoid update checks for third party software (cobook), dont want to "update" by mistake
The long term answer is to have the developer code sign their app in a manner that lets you can opt out of upgrades. Once you convince them why this is good, they will have the option to fix whatever issues you have with patching the app or allow their customers to control this.