Condenser failure mode would be a leak, though, which would stop the compressor due to low pressure.

If you start it up from "cold", you should feel the low pressure pipe mentioned getting cold quite quickly.
Also, the high pressure pipe, which is down in front of the aux. pullies - a little U shaped pipe with one of the fill valves on it, should start getting warm.
If this happens to start with, and there's some cooling, but it peters out, it could be that you have moisture in the refrigerant circuit that's freezing up and blocking it or that the expansion valve is allowing the evaporator to get so cold that it freezes up and restricts airflow through it.
If the pipes stay cold/hot respectively, but it's blowing warm air, it could be one of the blending flaps directing hot air into the cabin or the HBV not switching off the hot water flow.
If they don't stay or get hot/cold it could be the expansion valve not allowing the evaporator to get cold enough.
Ultimately, you probably need to get an aircon guy to measure the pressures and diagnose it that way but at least you can rule out any issues not related to the aircon circuit itself.
Why not take it back to the buy who refilled it? He might take a look FOC, especially considering it's an offence to fill a leaky system.