Track record, if they made wrong predictions about negative effects of the ERM / Euro then we can be more skeptical of the predictions of about leaving the EU.
Not that this is really what is debated, Gove states he discounted a view from some organisations on an issue because of their track record. Davey asserts Gove didn't discount their view for reasons stated but for other reasons, he can't possibly know that unless he is able to read minds.
Wrong Gove said we've had enough of experts - not just organisations that might have made some wrong calls in the past, but experts in general.
And you are wrong certainly on the Euro - don't forget that one of the key reasons why we didn't proceed with joining the Euro was opposition from the Treasury. So if joining the Euro would, with hindsight, have been the wrong decision then the Treasury called this absolutely right. So why was Gove dismissing the Treasury's view on Brexit then if he was only pointing to organisations that got it wrong in the past.
The reality is that the experts were pretty well unanimous, and opposed to Gove's view - hence he tried to make the case that we should dismiss experts.
But anyhow we are now in a period where we can see whether the experts or Gove (it will be all sunny and lovely) is right. So far looks like the experts have it. Indeed all of the predictions of what would happen immediately post-brexit are indeed happening. They were right all along.