I don't use Twitter for this reason. It is a way to quickly convey information but in business these sales are never final till the check clears. So discrepancies are likely but by omitting the other possible revenues this methodology should give a ballpark figure.
Having spoken with Arrayit they are well aware of invedtors attempt to estimate sales using Twitter. These are not stupid people so I doubt these figures are fabricated.
In addition, it would be pointless. They could tweet a 10 million sale and almost no seasoned investor would give it credence without something other than a tweet so pps would not be affected.