you need to get an electrician to do a portable appliance test on it now that you have knowlage that there may be a fault in it.
It might pass then it would be ok to sell it on knowing that it is safe.
If it fails it might be an easy fix but with the experience i have it will possibly be a faulty compressor then it is not ecconomical to repair and should be dumped as it could be a fire risk.
Sorry for the doom and gloom but have seen these go on fire in the past after being plugged into a circuit protected only by fuses instead of RCD`s, MCB`s or RCBO`s.
The reason that it doesn`t blow the fuse is that fuses can have a 100% overload capacity before they will blow and an RCD / RCBO will trip with only a 30mA fault.