@Nongnuch *******
Finally someone who knows what he's talking about.
I've been living , working and now visiting Thailand for over 30 years.
As you said , the best rates are in the basement near the airport link ticket office. As you also said , super rich do give very slightly better rates at their head office. Not only their head office though , their other downtown booths are also slightly better than their airport exchange booth but it is a miniscule difference.
Also the posters that keep repeatedly saying " you get the worst rates at airports , who would be so stupid to change money at an airport blah blah blah" . You people clearly don't know that downstairs in the basement the rates are totally different to the traps just before and after immigration.