I guess, arguably, that you have to be a little arrogant in order to sell. I can't imagine buying a flat or a house from a meek and apologetic estate agent.
Not only are they thick and arrogant but some of the ones in London sound so posh you'd swear they're related to the Queen. Nevertheless, I still wouldn't trust one further than I could throw 'em,... and hey, I can throw real far.