Very True.
Though I dont know many AC mechs, but have not seen/heard a single workshop that does the job "properly". Even if the main techie at the workshop is familiar with the procedures of repairing/servicing the Air Conditioning system, he does not bother to let his guys work like that. They just wash and clean the system and fit it back. And blame the Gas quality afterwards 
Any air-conditioning system if not properly vacummed, either home split or automobiles one, will not perform satisfactory. No matter which Gas you fill in with American/French/Chinese/Indian
Likewise refilling Gas (top-ups) and mending leaks here and there, without letting the compressor properly oiled will never let the system perform at its peak and also deteriorates the health of the compressor.
Company fitted ACs perform better, not because they have only original Gas, but mostly due to the properly fixed and filled Air Conditioning system.
Properly flushing, oiling, insulating, fixing and vacuuming the AC system is quite a time taking and technical job. May be people are not willing to pay that much for a justified job thats why people who do know, do not do the job as it should be done.
And oh yes, I know the above mentioned Sanden people of Karachi also, they do the same as like others too
One more thing I have seen (though I am not sure about this), AC guys always keep a low pressure (empty) Gas container with them. Before dismantling the system they just store back the available gas in their empty cylinder and fill it back with other cylinder, charging the customer for the whole Gas. One empty unit approx consumes 0.75-1.5 kgs of gas (depending upon the make/model) only. Every other AC guy have a Honeywell cylinder, which he gets filled from a wholesale distributor of Cooling Gas. R134 Refrigerant in the open market costs around 600-900 per kg depending upon their quality.
I used to get R22 refrigerant at the rate of Rs. 300 per kg from open market for my home ACs a couple of years back. But R22 is cheaper in rate in comparision to R134a.
