Hmmmm, tricky one this..
If your air con is just a bit tired but otherwise OK then there's very little Kwikfit can do to 'dangle berries' it up.
I had this decision to make with a Volvo. The a/c worked OK but not brilliant, so I deduced that it was not leaking due to the fact that there seemed to be sufficient gas to enable the compressor to run correctly.
I just felt it needed freshening up as there was no record of it ever having been vac'd out and recharged, as is considered good practice every three years or so.
Even the most simeon of fitters is able to hook up the machine, type in the vehicle details and leave it to do its own thing for an hour or so, which is as involved as it's necessary to get from their point of view.
You even get a print out of what's been recovered, how long and deep it's been held under vacuum and what new stuff has been put in.
The machine literally does it all on its own.
I wouldn't normally go to one of these places, but the Volvo's been fine ever since and I even blagged a deal on a couple of premium tyres while I was there. Got 'em fitted & balanced for same make / price as I could find mail order off t'internet or eBay...
They don't seem to try their tricks if you come across as a bit savvy, and not all their depots deserve the reputation the company's earned itself. Some are definitely and infinitely better than others.
Speaking as I found, I'd tread carefully but Carlisle was fine and I'd go there again if necessary.