Some points you make are correct, others not so.
Ford did not dump them on their arse after the Machargs takeover, nor did Arnold throw Ford out of Pollokshaws Road when they had a branch down there. Arnold took over Machargs (still Macharg, Rennie & Lindsay Ltd then) in 1986 when they were a Rover dealer, MRL remained called that until 2000, then shortened to Machargs, in 2003 First Ford (an amalgamated group of independent Ford dealers like Clanford, Wylies, Premier Ford, Alexanders who joined forces to create an enlarged group) went bust, Arnold took over the Paisley, Greenock, Anniesland and London Road branches, Anniesland was immediately sold off for housing and the Ford franchise relocated to Yorkhill Quay where their Daewoo franchise was, which moved to Alexandra Parade (then Mount Vernon but thats another story) eventually as part of the regeneration of the Clyde, Yorkhill Quay closed, and the Ford franchise moved to Machargs at Castlebank Street, around about the time Rover went bust, Machargs later moved to South Street where it still is, and around late 2014/early 2015 eventually changed name from Machargs to Arnold Clark.
The only franchises Arnold ever had on Pollokshaws Road were Vauxhall (originally Queens, taken over 1995) and Renault (now At Hillington, acquired 2002) he never had Ford in Pollokshaws, for years it was Wylies, who as i said amalgamated with other dealers to form First Ford, when it went bust Reg Vardy acquired the branches Arnold didnt (Pollokshaws, East Kilbride and Kirkintilloch) and in 2004 the lease ran out and Vardy closed it down, it got knocked down and flats built on it.
They didnt take over Harry Fairbairn as the new Mini was being launched, that was 2001, Arnold took them over in 2006, there are a few stories why its not called Arnold Clark, first one being simply the familiarity of HF to BMW, secondly BMW insisted back then that every dealer groups BMW franchises ran under a different name from the BMW dealers, when HF was independent, they had Honda, Fiat and Toyota dealerships just called Fairbairn Fiat etc. Parks Motor Groups BMW branches are Douglas Park, rest are called Parks, JM Group who ran the Belmont, Murray and Weir dealerships called their BMW dealerships Dunedin, Hyndland Honda and Queensborough Rover, Skoda, Daihatsu, Kia and Mazda owned a BMW dealer called Henry Bros, Macrae & Dicks BMW dealership was Menzies, Eastern Western Motor Groups BMW dealership was Eastern, all their other dealerships like Merc, VW, Honda, Toyota, Nissan, Mazda, Saab, Alfa Romeo Lexus, are all called Western. The only exception to this rule is Peter Vardy but its possible by 2007 when he first acquired his the rules had changed. The final story is Mr Fairbairns widow insisted a condition of the sale to Arnie was that they did not change the name of the business her husband had founded until after she had passed away.
The whole thing about AC staying out of the North of England is nonsense, they had dealerships there while Vardy still traded, and as for Vardy giving up branches to Arnold in Scotland, these were branches which either Vardy wanted to exit or didnt fit with their portfolio for example Aberdeen Fiat/Alfa when Arnold ran most of the other Fiat branches up that direction, or manufacturer territories and geographic areas, for example Vardy sold Renault in Pollokshaws and East Kilbride to Arnie as Arnie ran Renault in the rest of Glasgow, the EK branch became a Motorstore because Parks had been awarded the Lanarkshire territory and got Renault in EK to align with their Coatbridge, Hamilton and Motherwell Renault franchises.
The rest about owning a coachbuilders who produce the van bodies, owning a garage equipment company, and eventually acquiring control of GTG which was actually started as a collaboration of Arnie and other motor dealers in Glasgow is true, However to my knowledge they dont own Iain Semple Chemicals, Autoparts who are part of AC buy all their stuff from them and are his largest customer that much is true.
The squint plates comes from mechanics having to PDI cars in a rush constantly getting hit with PDIs late afternoon, or rush jobs for cars not PDId when the punter is waiting for their car in the showroom due to salesman incompetence not having his car prepped in plenty of time, or mechanics continually being pulled from one job to another, or mechanics or valeters being sent out to a compound with 30 cars to plate and obviously getting bored of the tedious monotony of it, or else being told they only have 90mins to plate 30cars, giving no time for measuring and lining them up accurately.
Arnie personally was a decent guy from what I know, but had lost his marbles a good 10-12 years ago, and wasnt the managing director even as far back as 1998 when Eddie Hawthorne got promoted to that role, Arnie may never have even had that role because in sure Glen Gall was the MD before Hawthorne, even in 1 large main dealership there would be a lot of dodgy practices by the staff that the owner would be largely unaware of if its kept hidden enough, if you then multiply that by 150 branches its suddenly easy to see why things were so bad, its not excusable but does explain why it happens, AC are too successful for their own good to the point they are so busy things get rushed, not done properly, or forgotten about or just not done, certainly in the branches I worked in the staff, except the odd couple of wideboy dodgy salesmen who were quickly moved on, did their best and tried their hardest from what i saw. I am in no way defending them as I was treated like ****e, I hate the company and they are not good to work for, just telling it like it is.
You will find other large dealers in my experience like Parks, Pendragon (Evans Halshaw) Reg Vardy, Abercromby, JM Group (Murray, Weir, Belmont) were just as bad, no better than Arnold, just smaller so you heard less about it, only the small indepedent franchises who survive on reputation in my experience are any good, the trouble is the manufacturers rip the franchises off them due to greed and give to big groups in the drive for more sales, or for some reason believe big groups controlling all their franchises in a particularly territory or operating less dealers each operating more dealerships is a more successful business model.