Are you connecting to the Mayfly directly using the onboard microUSB jack, or a separate FTDI adapter connected to the FTDI jack on the Mayfly? Are any LEDs powered on the Mayfly when you turn it on? I hand-check and program every Mayfly board when it leaves my workshop with a sketch that blinks the red and green LEDs and prints the temperature to the serial port every second at 9600 baud. Assuming the board hasn’t been reprogrammed by whoever sold it do you and that it’s still functional, you should see that kind of response from the board even before you attempt to program it yourself. Since you bought it on Ebay, I have no way of knowing whether the board is functional since the seller must have bought it from us on Amazon and is then reselling it. It’s definitely not an authorized, direct-from-EnviroDIY board.