Internal polls are often quite accurate
Again, Wulfric doesn't know what he's talking about. It's not as if every internal poll (especially the ones that are being released by a campaign) are always wildly off. Obama's and Trump's internal polling were probably spot on for the most part. Or think of McCaskill, Tester and Heitkamp in 2012.
Internal polls that are close to the final result are only so because the actual result happens to be friendlier to their candidate than the national independent polls project, not because of any type of superior methodology.
Internal polling is no more accurate than independent polling and is a whole lot more imprecise (biased) due to their tendency to be a few points too friendly to the candidate who hired them.
If an internal ends up close to the final result, great, but as a rule, they are not to be trusted.
Bare in mind that most internal polling is never released. Internals that are bad or no better than the polling companies' numbers are not released.