By crap design, do you mean something like this?
is it possible that the onboard arduino UNO serial to USB chip is interfering with data being received from the max232 chip that is sitting between the RFID receiver and the arduino UNO.
By crap design, do you mean something like this?Yes that is quite a crap design. There is no negative voltage generator. It won't work with a real RS232 interface but will probbly work with the crap ones you get on PCs.