Boundary Garage M.O.T.Testing

My car had battery issues, tested it myself and battery read 12.0v (which is dead) and after a jump start was reading 14.5v, alternator good!Took it to boundary garage for battery change and was told battery good just needs a charge- alternator knackered"... hmmTook it halfords and they agreed with me- new battery fitted at £120 and no issues since.Never received the quote for alternator but had phone calls asking me to bring my car in so they could change it. I'm assuming they wouldn't touch the alternator and just swap out the battery at around £800....These guys are con men. Shame as I have used them for years and never questioned them until now."