First off, you should smack the repair guys. They should never change setup of a connected device without authorization from the customer. If they do change it they should fill out a card that identifies the new setup information.

I did a lot of work with device communications over all sorts of connection paths and the way I handled user setup was I built an autodetect for the settings.

It takes a minute to cycle through the different baud rates and the guarantee the data for the speed is valid. Simply run through each baud rate and listen for 5 seconds. Tell the user the keep the scale empty for setup purposes. Check for 0lb0lb0lb in your string. This will keep any anomaly from happening from the mistranslated characters at different speeds.

Have an initialization feature so that whenever the repair guy comes, the user can run it. Also, I still say tell the repair guys to use a standard setting for this information. They should never be changing parity or stop bits either. Those are standard no parity 8 bits.