Is this a con

[BAGGGERS]

I went to Kwik fit for a ABSSensor fault, they said I have to go to a dealer because the diagnostic would not let them in. 
I then went to another garage, they said the same, diagnostic would not let them in. 
I went to WJ King they said either the other garages had the wrong equipment or were not qualified to carry out the work. I’ve booked the car in on a Tuesday morning And 24 hours later they told me it was the ABS sensor which I already told them and they want £144 for telling me the information. They then said the ABS sensor was seized up in my 70 reg car and needed to be replaced with the other sensor on the front to check it and that would cost me another £220 totalling £360 and that still might not be the problem if it wasn’t I would have to pay more. I said it could go into thousands of pounds he said well yes that’s possible I asked if the diagnosis showed anything other than the ABS sensor he said no . 
I don’t understand why I am paying £144 for a diagnostic. I already told them when I went into the dealers and also showed on the dashboard in writing.

What’s your opinion on this?

[Vauxhall Owners Club]

Thats completely unacceptable.....an old school mechanic can measure resistance of sensors to further confirm that a sensor is defective. 
Sometimes, just contamination in a sensor connection or even damage to the reluctor ring (if seperate - e.g. not part of the wheel bearing) can cause fault codes and replacing the sensor is meaningless.

I would take the car to a good 'old school' independent garage who can diagnose the fault correctly