clio extreme as new ecu fitted

evening guys and girls, help is needed !! bought my daughter a 2002 clio extreme ,on delivery i found that the air bag and service light were staying on plus no radio code , he took the car away for repair,great !! then contacted me to say it was the ecu and he has fitted a new one but how will i know he has, or just not cut the wires or bodged it up ,what am i looking for ??

cheers norm

ps should all the dash lights come on then go out??