A decent quality wall wart with the specs he is posting should not damage the unit.
Current is a function of the device being powered so ideally, using a 450mA supply with the proper voltage will not be any different than a 100mA supply if the device doesn't draw more than 100mA. In other words, the power supply is a voltage device and provides 24 volts and the unit draws as mush current as it needs. So a higher rated power supply at the same voltage should not be a problem. However, when wall warts are underloaded they can provide higher than listed voltage.
Most likely, in my opinion, using the "incorrect" power supply would not damage the unit even if it is providing slightly higher than designed voltage. However, I would not refund the money unless he has tried the proper power supply.
Those specs on the Paradigm model are interesting though. It says it provides 100mA at 24 Volts which would be 2.4 Watts but it says it's rated for 4 Watts. On the model the buyer has described, it's 450mA at 24 Volts which is 10.8 Watts...very close to the stated power rating.
(I'm assuming all values are provided in RMS, which is typical unless specified otherwise)