I returned a hire car at 2.00 am and had to get home from BKK. Grab price was 440 baht for standard car, 11 minutes wait or 500 and something for priority. I decided to give the taxis a go. Meter price was 190 plus the 50 airport fee, so 240...I gave 300. I bit of a win for both of us I thought. I'll note that we had no baggage and my GF is thai. Not sure if that reduced the chances of being scammed or not.