[mothered]

You're SEing Amazon Itself, so It's a given Item In their Inventory that your wrong Item Is based on.

One last thing, how closely weighted do the items have to be without arousing suspicion? ( just a rough estimation would help as I know it differs from case to case) Having trouble finding a return item that weighs exactly the same

Is there a way to know how much your parcel weighed at consignment leaving the amazon warehouse? Or is that only known to amazon and the courier and you’d have to physically weigh your parcel when it arrives to find out. Any ideas?

They weigh and dispatch It, so you have no knowledge of that.

What your concern Is the weight of the "Item", namely when using the wrong Item received method.