Inventory Reconciliation

Been having an issue with Inventory since last year.  Have spoken to specialists at MYOB, but nothing seems to be helping the issue, just wondering if anyone else out there is having the same issues.

We 'purchase' goods from our customers when we invoice them, so effectively do a credit against the inventory item.  We then resell it, using a different inventory item.  I have been doing transfers of the stock on hand through adjust inventory, but it seems to be messing up the totals.

As you can see by the attached screenshots, this is just one example, the buying and selling cost are one figure, the invoice is correct using those figures, but in the general ledger it is appearing as a completely different figure, and I am trying to work out the best way to fix it.

MYOB have suggested resetting each invoice by putting a . in the journal item.  It does change the figure but not to what it should be.

Does anyone else have these issues, or know of a way around it, or would i be better off doing it all manually and journalling?  (not an option I really want to consider!).

Any assistance would be greatly appreciated