Sample case
Photographer sends film to a mini lab that processes via roller transport, but then scans and applies Digital Ice program to hide dust and scratches.
(Digital Ice programs were available to the large and mini labs for over 15 years.)
They then pull off brilliant 4x6 proof prints or even 8x10 prints, photographer is very happy .
Two years later , photographer comes to me with their cherished images, and ask me to make a series of 16 x20 silver gelatin prints.
I make the prints on my condenser enlargers, with Apo lenses, with level glass carriers resulting in beautiful prints with heavy scratches due to scratching in process.
Client thinks I am a shit, because the proofs were lovely but the prints are scratched , and I have already charged them for my services.
Very early in my printing for others day this was a common occurrence , if it wasn't scratches from other labs it was improper processing that usually resulted in poor shadow detail.
What is a poor boy to do, WELL I started to refuse foreign film negatives (film processed by others) , I was called arrogant, snobbish, reclusive,, ***Dinesh can add a few more names***.
This indeed started an exclusive club of clients who had me process, contact, scan and print only for them, it works and today I have clients that have been working with me with film and paper since 1991 till now.
Today this has changed for the good in my life as most files we print have been retouched and expectations are quantifiable. If I am printing from negatives it is very probable I have processed the film and can only look at myself if there is a problem.
I have kept my prices consistent to the other labs, and unlike Millers my doors are always open to walk in clients without accounts, but as you see from above I do have my policy's in place that can cause issues to clients expecting something different than what I offer.
GTA Imaging in Toronto is exactly like Millers and they offer top rate service to clients like the OP , but they have a pay up front policy (which I really like) but they do not offer film services, and No I do not provide those services for them.
Their pricing structure is based on long term client loyalty and that is what the OP is suggesting here. They have adjusted their markup to reflect continuous loyalty, much like Starbucks or even better Tim's. (for non Canadians, Tim's is a monster coffee chain here - started by the late great Toronto Maple Leaf defenceman Tim Horton.
I see nothing wrong with these models of Labs, in fact my first job in photofinishing was that of custom printer for Custom Colour Labs, here in Toronto, and I printed the large custom prints for commercial photographers across Canada and into the States. There was no walk in clients and everyone was on Account , and we were 40% cheaper than the more niche labs in town.
Like Omar (CatLabs) suggests , at least I think he is suggesting
We will eventually end up with large Labs like Millers or GTA's spread out over NA where the photographer will send out work and get it back in due course and be able to up charge the service and make the spread.
Or, smaller niche labs like mine, Toronto Image Works, Icon who service a professional, art, and retail client base .
Not to mention there will always be Mini-labs offering cheap and cheerful ink jet prints on systems to make you happy , happy , happy.
Just do not expect your local mini lab to offer you quality film process, or high end editing , printing services.
Not much has changed over the last 50 years , except the fact that the Manufactures (Epson, Cannon, Nikon, HP, Phase) (Sony, IPhone, Flicker) (Adobe Elements Lightroom Photoshop} has made photography assessable , easy , fun, safe, sexy , for every person on the globe today. There is good and bad elements .
But do not be mistaken, before digital there was 100, krillion trillion negatives shot that did not deserve the light of day, We are (capturing) a huge percentage more images today, but thankfully they are not being printed, but ending up on the web.