It's very standard for an advisor in sale/acquisition to be appointed as non-exec. The principal reason for this is obviously their specific knowledge and contact base and what they bring to the table in that speciality but also they can act with more impartiality. So, take Levy who could be emotionally invested in Spurs (he's been at the Club 20yrs and built it from mid-table to top 4 and top 10 in Europe, he's also a fan of the Club).
Flip the coin and the above means potential buyers are more susceptible to their communication (he'll have his own book of trusted contacts/potential buyers who trust his judgements), by being a non-exec he'll also have an very in-depth view of the Spurs which those contacts will trust. That said, and to blow that statement apart I see in his bio that he was involved in the sale of Autonomy to HP, which was reported as fraudulent as the sales/revenue was supposed to be massively overinflated by Autonomy resulting in them in overpaying by a few billion!
