Do you expect a small garage to buy a car, spends hundreds fixing it, get it MOT'd, and then try and sell it for a profit? It's simply not possible. Big garages get cars far cheaper than little garages, so the price ghets pushed up meaning there's almost no profit in car sales for smaller garages anyway.
I'll tell you now that a small garage will do any work you want them to before it's sold, as it's a fucking nightmare is someone's constantly coming back wanting work done. Bigger garages don't do any more work before they sell a car, they generally do nothing as it's all about turnover. They just get newer cars, with less problems, for far less. Leaving them a huge profit, a high chance that there won't be any problem for a while after the cars been sold and also a huge margin if anything does go wrong
You seem to be suggesting small companies are all about the money and would rather shaft you than help you, when it's the complete opposite for most. You'll bound to find a garage of dodgy traders. But the majority of small garages are fighting everyday to try and make a profit. The Audi garage in Perth makes a profit of almost £500k a month from labour and parts alone. To try and compare a garage like that to a small independent is completely foolish, and for what its worth your customer service would be far better at a small garage. The bigger ones are all about profit, and trying to kill the smaller ones off, this is why you see so many finance deals at the moment. Small garages cant compete