Just look at the damage caused to the credibility of the Teesworks as a result of him handing 90% to his associates in a secret deal. This was criticised in the corruption report although he did not recieve a brown envelope. On the face of it he has done somthing similar with the South Side, which I think had no tendering process, but he wont even indicate if any payment was recieved. It may have been a great deal for the taxpayer and the airport but we may never know and the uncertainty gives ammunition to the airports critics.
There has been much criticism that he has only attracted holiday flights that are of little economic benefit to the region but may help him win an election. Why refuse to answer questions about the basics of a deal (not the actual amounts involved) and shut the critics up.