Look at it this way. If every purchaser understands up front that they are going to get 950g in each pack, then if they order 3 they only need to send a 3kg bag next time and not a 5k, and if they order 4 or 5 then they only need to send the 5kg bag, as the satchels will then come in at legal weight, so they have saved themselves at least $2 per kilo immediately. For the sake of 50g they are dollars and dollars ahead. That being the case we will then refer to the packs from there on as 'repacks' rather than 'kilos'. It would then be crazy not to order either 3 repacks or 5 repacks, if you are concerned about postage costs. It also eases the dust problem and means that Graham doesn't have to do arcane calculations re 'slippage' when ordering the bulk quantity from China.
Chappo: thank Tidal Pete who was the main architect, and Graham of course. I only provided the beer
Edit: on the subject of scales calibration, next packing day if someone could just bring along a kilo pack of ALDI rice and have a weigh around at the beginning, that should solve that one.