I’ll elaborate only a little, because the explanation and previous assertions from you - and from me, were overly simplistic.
MM doesn’t simply protect you from a manufacturer denying warranty coverage for non OEM consumable use, it protects you from shady dealers, and cheaply made or engineered vehicles, when the vehicle starts to exhibit higher than normal failure rates and the regional reps start driving efforts to ‘find a reason- any reason’ to deny warranty coverage. As you previously alluded to in another thread about denying a warranty claim for an obvious incidental modification.
This is true. In fact, notorious in brands like Kia/Hyundai with their 100K warranty. The vehicles tend to have significant issues by 100K miles, so they will pull any excuse to not cover the repair. I have seen this first hand in Ford/Kia dual franchise stores.
MM insulates you from bad actor “policies" - which you’ve indicated largely come from the dealer side - mech., S/A or S/M giving the blanket ‘abuse’ declaration or warranty voided because of some incidental mod. That kind of stuff is stupidity on a grand scale, but again it happens. If your service department is fishing for a reason to deny your warranty coverage, MM can protect you in some cases. We’ve practically all been victimized by something similar at some point.
You are correct, it does happen. There are 2 extremes - "mod friendly" dealers (the vast majority of which are committing warranty fraud) and those that look for any reason to void a warranty - typically because they are not on good standing with the manufacturer's warranty division. If they refuse to warranty anything and claim it's all "customer pay", nothing can get charged back! Easy way out. In my experience, the people claiming "no warranty" are service advisors and don't have the slightest clue what they're even looking at.
Now, things are vastly different. Most dealers value the customer service feedback and actively solicit you to give online reviews and what not. This is rapidly becoming a pretty good tool to use for both good and bad experiences. It used to be if you got a bad experience from the dealer, you were SOL. Now, you can actually drive business away just by being honest on the internet. I think this, and not lawsuits, is the death knell of the alpha hotel service manager or service advisor. Online comments like “I’d go there but the service manager yelled at me and made me feel dumb” goes a long way to driving business elsewhere.
I hear that. I saw a Ford dealer near me that had 1 star reviews online...every time someone would write a bad review, the dealer representative would reply that it was a one-off and the customers fault. Next thing I know the dealer goes through a "buy/sell"...meaning Ford terminated the franchise and forced them to sell to another owner.