Best practices means you find a way without trying to screw your customers.
I'm not sure that qualifies as "trying to screw your customers". Agreeing on a price, then sneaking in all sorts of extras that weren't mentioned is screwing the customer. Claiming that the warranty is voided by the customer servicing his own vehicle is screwing the customer. Tricking the customer into signing finance applications with 3 different loan companies is screwing the customer*.
But any item is worth exactly what a buyer and seller agree it is worth on any given day. Sounds like this dealer was upfront about pricing. The customer was free to disagree and look elsewhere. It may be a poor business strategy, but then, maybe that dealer felt screwing over his employees by cutting wages was a worse strategy -- there's another thread going on pointing out the shortage of good mechanics and the need for dealerships to offer competitive wages in order to attract and retain experienced people.
*This actually happened to my son. He bought a used car at a fair price. Call it $10k after trade-in, but I forget the exact amount. The salesman would handle all the financing, just sign the paperwork here, here and here and drive it off the lot.
Turns out the paper in triplicate was turned into 3 separate applications for the full $10k to 3 different banks, putting the kid on the hook for $30k. His first inkling of trouble was when each bank sent him the approvals a few weeks later. If that wasn't bad enough, it turned out the dealership didn't even own the car -- it was a leased vehicle and GM wanted it back!
In the end, that was his salvation. It proved intent and got him off the hook for the loans since the sale was fraudulent. He even eventually got his trade-in back (despite that having been sold to another patsy in the meantime), since it formed part of the fraudulent sale.
Now THATS screwing the customers.