Weighing items after purchase

I have recently heard that in order for the sale of meat/fruit/ items sold by weight to be halaal the buyer either has to be present to see the item being weighed or has to ask for R200 worth of mutton instead of 1 kg of mutton. I order my meat from a butcher telephonically and order by weight as I am generally aware of the meat prices. This is then delivered to my house and later paid for. In this instance is the meat halaal as I have been told it is haraam?