I have some cheap luggage scales from Asda. I’ve taken them to the shop and tested them with all the standard weights we use for testing the shop scales and they were surprisingly accurate (I figured for a couple of quid they’d be well out). Ryan Air and BA also agree and the nice man who comes around to check our ‘weights and measures’ said he was shocked that something so cheap was accurate.
So whatever you buy and use make sure you test them with some objects that you know the weight of to see how accurate they are as it’s possible even expensive scales could be wrong or need recalibrating.
Tom KP