I also bought my car from Arnold Clark, and this seems typical. In general, if the car is in reasonable condition then AC is a good bargain. If there's anything wrong with it then their customer services go beyond awful into vindictive. Their general attitude is: we have your money, so **** you. In my case I test drove the car, and it was fine. Sold my old car the day I'd agreed to pick up the new one, which needed wheels refurbing and a service. The day I was due to collect it AC phoned to say it had failed an MOT due to a broken spring. Which was very odd, because they'd MOT'ed it two weeks earlier, before I drove it. Further, the spring certainly wasn't broken on the test drive: no noises, no weird steering or braking, nothing. But hey, broken spring. Except they wouldn't give me a courtesy car, and wouldn't even go halves on a hire car (bear in mind they have a hire car division). I even ended up talking to the local manager senior sales manager who essentially told me: you signed the paper, we stopped caring.
So I had to hire a car for a week at my own expense while they tried to find a spring. The good news is that it was a genuine Merc spring (which were then, and still are, really hard to find), the bad news is that the cheap ******* only replaced the one that broke, not the pair, so the other one broke eighteen months later. I'm pretty certain that the spring got broken when they had the wheels off for refurb - but I can't prove it.
The stupid thing is that there's a core of good service there at AC. But only until something goes wrong, then they screw you. The staff are great, and the woman who sold me the car spent ages apologising for her manager. But I will still never deal with them ever again. And I advise everyone else the same.