I use my el cheapo home scales and they are right on when the bags are weighed at the airport.

I travelled on an Alitalia domestic flight (Naples to Venice) a few weeks ago and one of our bags was 23kg but they didn't say anything.

For a summer holiday (2-4 weeks) we always take 2 medium sized suitcases & they always (with lots of books, toiletries etc) come in at between 20 & 25kg each.

<<< Huh? Then they need a decent bathroom scales. Are you suggesting it may be off by several pounds? If so, it isn't a good scales. Pure and simple. >>>

The spring ones can be very inaccurate - even shifting your weight from one foot to another or from ball to sole can give readings that differ by several pounds